diff --git a/packages/embeds/embed-core/src/embed.ts b/packages/embeds/embed-core/src/embed.ts
index c39dbf2d00..7dcbcddd18 100644
--- a/packages/embeds/embed-core/src/embed.ts
+++ b/packages/embeds/embed-core/src/embed.ts
@@ -483,7 +483,9 @@ export class Cal {
         // linkReady event isn't received anyway by parent as it isn't whitelisted to be sent to parent but it is a safe guard
         return;
       }
-      this.iframe!.style.visibility = "";
+      if (this.iframe) {
+        this.iframe.style.visibility = "";
+      }
 
       // Removes the loader
       // TODO: We should be using consistent approach of "state" attribute for modalBox and inlineEl.
@@ -1052,7 +1054,7 @@ class CalApi {
     const { embedConfig: previousEmbedConfig, embedRenderStartTime: previousEmbedRenderStartTime } =
       this.cal.getPreviousModalRenderStartVariables();
 
-    let enrichedConfig;
+    let enrichedConfig: PrefillAndIframeAttrsConfig;
     const configWithGuestKeyAndColorScheme = withColorScheme(
       Cal.ensureGuestKey({
         ...config,
@@ -1061,7 +1063,7 @@ class CalApi {
       containerEl
     );
 
-    let enrichedPrerenderOptions;
+    let enrichedPrerenderOptions: ModalPrerenderOptions | undefined;
     if (isPrerendering) {
       const preparationResult = this.cal.prepareForPrerender({
         calLink,
@@ -1578,7 +1580,7 @@ document.addEventListener("click", (e) => {
   const namespace = calLinkEl.dataset.calNamespace;
   const configString = calLinkEl.dataset.calConfig || "";
   const calOrigin = calLinkEl.dataset.calOrigin || "";
-  let config;
+  let config: PrefillAndIframeAttrsConfig;
   try {
     config = JSON.parse(configString);
   } catch {
@@ -1602,7 +1604,7 @@ document.addEventListener("click", (e) => {
   });
 
   function getCalLinkEl(target: EventTarget | null) {
-    let calLinkEl;
+    let calLinkEl: HTMLElement | Element | undefined;
     if (!(target instanceof HTMLElement)) {
       return null;
     }
@@ -1641,7 +1643,7 @@ let currentColorScheme: string | null = null;
 })();
 
 function getEmbedApiFn(ns: string) {
-  let api;
+  let api: GlobalCalWithoutNs | GlobalCal;
   if (ns === DEFAULT_NAMESPACE) {
     api = globalCal;
   } else {
diff --git a/packages/lib/CalendarService.ts b/packages/lib/CalendarService.ts
index e8ea2d1c14..04effe1d9e 100644
--- a/packages/lib/CalendarService.ts
+++ b/packages/lib/CalendarService.ts
@@ -458,9 +458,9 @@ export default abstract class BaseCalendarService implements Calendar {
           startDate.second = event.startDate.second;
           const iterator = event.iterator(startDate);
           let current: ICAL.Time;
-          let currentEvent;
-          let currentStart = null;
-          let currentError;
+          let currentEvent: ReturnType<typeof event.getOccurrenceDetails> | undefined;
+          let currentStart: ReturnType<typeof dayjs> | null = null;
+          let currentError: string | undefined;
 
           while (
             maxIterations > 0 &&
diff --git a/packages/lib/CloseCom.ts b/packages/lib/CloseCom.ts
index 23b00c7f96..047787339a 100644
--- a/packages/lib/CloseCom.ts
+++ b/packages/lib/CloseCom.ts
@@ -257,8 +257,8 @@ export default class CloseCom {
         body: new URLSearchParams({
           grant_type: "refresh_token",
           refresh_token: this.refresh_token,
-          client_id: process.env.CLOSECOM_CLIENT_ID!,
-          client_secret: process.env.CLOSECOM_CLIENT_SECRET!,
+          client_id: process.env.CLOSECOM_CLIENT_ID ?? "",
+          client_secret: process.env.CLOSECOM_CLIENT_SECRET ?? "",
         }),
       });
 
diff --git a/packages/lib/availability.ts b/packages/lib/availability.ts
index f5db09f3f3..78254b1e3b 100644
--- a/packages/lib/availability.ts
+++ b/packages/lib/availability.ts
@@ -31,7 +31,7 @@ export function getAvailabilityFromSchedule(schedule: Schedule): Availability[]
       } as Availability);
 
     const filteredTimes = times.filter((time) => {
-      let idx;
+      let idx: number;
       if (
         (idx = availability.findIndex(
           (schedule) =>
diff --git a/packages/lib/components/ServerTrans.tsx b/packages/lib/components/ServerTrans.tsx
index 83a477216e..e83336bf06 100644
--- a/packages/lib/components/ServerTrans.tsx
+++ b/packages/lib/components/ServerTrans.tsx
@@ -245,7 +245,7 @@ const parseObjectComponents = (content: string, components: Record<string, React
 
   // Find all placeholders in order
   const placeholderRegex = /__(?:INTERP|TAG)_[^_]+_[a-z0-9]+__/g;
-  let match;
+  let match: RegExpExecArray | null;
 
   while ((match = placeholderRegex.exec(processedContent)) !== null) {
     const [placeholder] = match;
@@ -346,11 +346,11 @@ const parseHtmlTags = (content: string): ReactNode[] => {
 
   // Find all placeholders in order
   const placeholderRegex = /__HTML_[^_]+_[a-z0-9]+__/g;
-  let match;
+  let match2: RegExpExecArray | null;
 
-  while ((match = placeholderRegex.exec(processedContent)) !== null) {
-    const [placeholder] = match;
-    const index = match.index;
+  while ((match2 = placeholderRegex.exec(processedContent)) !== null) {
+    const [placeholder] = match2;
+    const index = match2.index;
 
     // Add text before placeholder
     if (index > lastIndex) {
diff --git a/packages/lib/hooks/useUrlMatchesCurrentUrl.ts b/packages/lib/hooks/useUrlMatchesCurrentUrl.ts
index b399212496..73c69afee2 100644
--- a/packages/lib/hooks/useUrlMatchesCurrentUrl.ts
+++ b/packages/lib/hooks/useUrlMatchesCurrentUrl.ts
@@ -10,7 +10,7 @@ export const useUrlMatchesCurrentUrl = (url: string, matchFullPath?: boolean) =>
   const pathname = usePathname() as null | string;
   const searchParams = useCompatSearchParams();
   const query = searchParams?.toString();
-  let pathnameWithQuery;
+  let pathnameWithQuery: string | null;
   if (query) {
     pathnameWithQuery = `${pathname}?${query}`;
   } else {
diff --git a/packages/lib/isOutOfBounds.tsx b/packages/lib/isOutOfBounds.tsx
index d385227d3c..f1aa944a47 100644
--- a/packages/lib/isOutOfBounds.tsx
+++ b/packages/lib/isOutOfBounds.tsx
@@ -183,7 +183,7 @@ export function getRollingWindowEndDate({
   const log = logger.getSubLogger({ prefix: ["getRollingWindowEndDate"] });
   log.debug("called:", safeStringify({ startDay: startDateInBookerTz.format(), daysNeeded }));
   let counter = 1;
-  let rollingEndDay;
+  let rollingEndDay: ReturnType<typeof startDateInBookerTz.startOf> | undefined;
   const startOfStartDayInEventTz = startDateInBookerTz.startOf("day");
   // It helps to break out of the loop if we don't find enough bookable days.
   const maxDaysToCheck = ROLLING_WINDOW_PERIOD_MAX_DAYS_TO_CHECK;
diff --git a/packages/lib/schedules/transformers/for-atom.ts b/packages/lib/schedules/transformers/for-atom.ts
index fd09ff3a4f..933fedabb7 100644
--- a/packages/lib/schedules/transformers/for-atom.ts
+++ b/packages/lib/schedules/transformers/for-atom.ts
@@ -52,8 +52,7 @@ export function transformDateOverridesForAtom(
     };
     const dayRangeIndex = acc.findIndex(
       // early return prevents override.date from ever being empty.
-      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      (item) => yyyymmdd(item.ranges[0].start) === yyyymmdd(override.date!)
+      (item) => override.date && yyyymmdd(item.ranges[0].start) === yyyymmdd(override.date)
     );
     if (dayRangeIndex === -1) {
       acc.push({ ranges: [newValue] });
diff --git a/packages/lib/server/PiiHasher.ts b/packages/lib/server/PiiHasher.ts
index 04cd57363a..a60c5c29ac 100644
--- a/packages/lib/server/PiiHasher.ts
+++ b/packages/lib/server/PiiHasher.ts
@@ -28,7 +28,7 @@ export class Md5PiiHasher implements PiiHasher {
   }
 }
 
-export const piiHasher: PiiHasher = new Md5PiiHasher(process.env.CALENDSO_ENCRYPTION_KEY!);
+export const piiHasher: PiiHasher = new Md5PiiHasher(process.env.CALENDSO_ENCRYPTION_KEY ?? "");
 
 export const hashEmail = (email: string, hasher: PiiHasher = piiHasher): string => {
   const [localPart, domain] = email.split("@");
diff --git a/packages/lib/smsLockState.ts b/packages/lib/smsLockState.ts
index 336d15d416..1e904e9196 100644
--- a/packages/lib/smsLockState.ts
+++ b/packages/lib/smsLockState.ts
@@ -23,7 +23,7 @@ export async function checkSMSRateLimit({
 }
 
 async function changeSMSLockState(identifier: string, status: SMSLockState) {
-  let userId, teamId;
+  let userId: number | undefined, teamId: number | undefined;
 
   if (identifier.startsWith("sms:user:")) {
     userId = Number(identifier.slice(9));
@@ -61,4 +61,4 @@ async function changeSMSLockState(identifier: string, status: SMSLockState) {
       },
     });
   }
-}
\ No newline at end of file
+}
diff --git a/packages/trpc/react/trpc.ts b/packages/trpc/react/trpc.ts
index d6f16dc654..cbf2d94075 100644
--- a/packages/trpc/react/trpc.ts
+++ b/packages/trpc/react/trpc.ts
@@ -30,7 +30,7 @@ const resolveEndpoint = (links: any) => {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   return (ctx: any) => {
     const parts = ctx.op.path.split(".");
-    let endpoint;
+    let endpoint: keyof typeof links;
     let path = "";
     if (parts.length == 2) {
       endpoint = parts[0] as keyof typeof links;
diff --git a/packages/trpc/server/routers/apps/routing-forms/formMutation.handler.ts b/packages/trpc/server/routers/apps/routing-forms/formMutation.handler.ts
index cbe6d6dbdd..97f4bba27c 100644
--- a/packages/trpc/server/routers/apps/routing-forms/formMutation.handler.ts
+++ b/packages/trpc/server/routers/apps/routing-forms/formMutation.handler.ts
@@ -363,7 +363,8 @@ export const formMutationHandler = async ({ ctx, input }: FormMutationHandlerOpt
       });
     }
 
-    let fields, routes;
+    let fields: NonNullable<typeof fieldsParsed.data>,
+      routes: NonNullable<typeof routesParsed.data>;
     if (shouldConnect) {
       routes = [
         // This connected route would automatically link the fields
diff --git a/packages/trpc/server/routers/loggedInViewer/teamsAndUserProfilesQuery.handler.ts b/packages/trpc/server/routers/loggedInViewer/teamsAndUserProfilesQuery.handler.ts
index 6b2dd38f5d..4d9f6f62ce 100644
--- a/packages/trpc/server/routers/loggedInViewer/teamsAndUserProfilesQuery.handler.ts
+++ b/packages/trpc/server/routers/loggedInViewer/teamsAndUserProfilesQuery.handler.ts
@@ -67,7 +67,7 @@ export const teamsAndUserProfilesQuery = async ({ ctx, input }: TeamsAndUserProf
     throw new TRPCError({ code: "INTERNAL_SERVER_ERROR" });
   }
 
-  let teamsData;
+  let teamsData: typeof user.teams extends (infer T)[] ? (T & { team: T extends { team: infer U } ? U & { metadata: ReturnType<typeof teamMetadataSchema.parse> } : never })[] : never;
 
   if (input?.includeOrg) {
     teamsData = user.teams
diff --git a/packages/trpc/server/routers/viewer/attributes/edit.handler.ts b/packages/trpc/server/routers/viewer/attributes/edit.handler.ts
index 960b37d8d1..aa70103778 100644
--- a/packages/trpc/server/routers/viewer/attributes/edit.handler.ts
+++ b/packages/trpc/server/routers/viewer/attributes/edit.handler.ts
@@ -103,8 +103,8 @@ const editAttributesHandler = async ({ input, ctx }: GetOptions) => {
   await validateOptionsBelongToAttribute(options, attributes.id);
 
   await prisma.$transaction(async (tx) => {
-    const updateOptions = options.filter((option) => option.id !== undefined && option.id !== "");
-    const updatedOptionsIds = updateOptions.map((option) => option.id!);
+    const updateOptions = options.filter((option): option is typeof option & { id: string } => option.id !== undefined && option.id !== "");
+    const updatedOptionsIds = updateOptions.map((option) => option.id);
     // We need to delete all options that are not present in this UpdateOptions.id (as they have been deleted)
     await tx.attributeOption.deleteMany({
       where: {
@@ -159,10 +159,9 @@ async function validateOptionsBelongToAttribute(
   options: ZEditAttributeSchema["options"],
   attributeId: string
 ) {
-  // We have to use ! here to make sure typescript knows that the id is not undefined
   const optionsWithId = options
-    .filter((option) => option.id !== undefined && option.id !== "")
-    .map((option) => option.id!);
+    .filter((option): option is typeof option & { id: string } => option.id !== undefined && option.id !== "")
+    .map((option) => option.id);
 
   // Check all ids of options passed in are owned by the attribute
   const optionsWithIdOwnedByAttribute = await prisma.attributeOption.findMany({
diff --git a/packages/trpc/server/routers/viewer/auth/resendVerifyEmail.handler.ts b/packages/trpc/server/routers/viewer/auth/resendVerifyEmail.handler.ts
index 86b2225cc0..eefcfc221c 100644
--- a/packages/trpc/server/routers/viewer/auth/resendVerifyEmail.handler.ts
+++ b/packages/trpc/server/routers/viewer/auth/resendVerifyEmail.handler.ts
@@ -28,7 +28,7 @@ export const resendVerifyEmail = async ({ input, ctx }: ResendEmailOptions) => {
   });
 
   let emailVerified = Boolean(ctx.user.emailVerified);
-  let secondaryEmail;
+  let secondaryEmail: Awaited<ReturnType<typeof prisma.secondaryEmail.findUnique>> | undefined;
   // If the input which is coming is not the current user's email, it could be a secondary email
   if (input?.email && input?.email !== ctx.user.email) {
     secondaryEmail = await prisma.secondaryEmail.findUnique({
diff --git a/packages/trpc/server/routers/viewer/bookings/editLocation.handler.ts b/packages/trpc/server/routers/viewer/bookings/editLocation.handler.ts
index db81d31e78..808d6b6f83 100644
--- a/packages/trpc/server/routers/viewer/bookings/editLocation.handler.ts
+++ b/packages/trpc/server/routers/viewer/bookings/editLocation.handler.ts
@@ -134,7 +134,7 @@ async function getAllCredentialsIncludeServiceAccountKey({
 }) {
   const credentials = await getUsersCredentialsIncludeServiceAccountKey(user);
 
-  let conferenceCredential;
+  let conferenceCredential: Awaited<ReturnType<typeof CredentialRepository.findFirstByIdWithKeyAndUser>> | undefined;
 
   if (conferenceCredentialId) {
     // Validate that the credential is accessible before fetching it
diff --git a/packages/trpc/server/routers/viewer/calendars/setDestinationCalendar.handler.ts b/packages/trpc/server/routers/viewer/calendars/setDestinationCalendar.handler.ts
index 0b1044ef75..20ce287fa2 100644
--- a/packages/trpc/server/routers/viewer/calendars/setDestinationCalendar.handler.ts
+++ b/packages/trpc/server/routers/viewer/calendars/setDestinationCalendar.handler.ts
@@ -74,7 +74,7 @@ export const setDestinationCalendarHandler = async ({ ctx, input }: SetDestinati
 
   const { credentialId, delegationCredentialId } = firstConnectedCalendar || {};
 
-  let where;
+  let where: { eventTypeId: number } | { userId: number };
 
   if (!credentialId && !delegationCredentialId) {
     throw new TRPCError({ code: "BAD_REQUEST", message: `Could not find calendar ${input.externalId}` });
diff --git a/packages/trpc/server/routers/viewer/delegationCredential/toggleEnabled.handler.ts b/packages/trpc/server/routers/viewer/delegationCredential/toggleEnabled.handler.ts
index a5b45b52cb..d1a061ce64 100644
--- a/packages/trpc/server/routers/viewer/delegationCredential/toggleEnabled.handler.ts
+++ b/packages/trpc/server/routers/viewer/delegationCredential/toggleEnabled.handler.ts
@@ -82,8 +82,8 @@ export async function toggleDelegationCredentialEnabled(
       log.error(`Delegation credential ${input.id} has no workspace platform slug`);
     }
 
-    let calendarAppName;
-    let conferencingAppName;
+    let calendarAppName: string;
+    let conferencingAppName: string;
 
     if (slug === "google") {
       calendarAppName = "Google Calendar";
diff --git a/packages/trpc/server/routers/viewer/eventTypes/util.ts b/packages/trpc/server/routers/viewer/eventTypes/util.ts
index 2197323ec6..2a80a9a117 100644
--- a/packages/trpc/server/routers/viewer/eventTypes/util.ts
+++ b/packages/trpc/server/routers/viewer/eventTypes/util.ts
@@ -176,9 +176,9 @@ export const createEventPbacProcedure = (
         const isAllowed = (function () {
           if (event.team) {
             const allTeamMembers = event.team.members.map((member) => member.userId);
-            return input.users!.every((userId: number) => allTeamMembers.includes(userId));
+            return input.users?.every((userId: number) => allTeamMembers.includes(userId)) ?? true;
           }
-          return input.users!.every((userId: number) => userId === ctx.user.id);
+          return input.users?.every((userId: number) => userId === ctx.user.id) ?? true;
         })();
 
         if (!isAllowed) {
diff --git a/packages/trpc/server/routers/viewer/me/updateProfile.handler.ts b/packages/trpc/server/routers/viewer/me/updateProfile.handler.ts
index c5b3fd4005..e587f27eb4 100644
--- a/packages/trpc/server/routers/viewer/me/updateProfile.handler.ts
+++ b/packages/trpc/server/routers/viewer/me/updateProfile.handler.ts
@@ -329,7 +329,7 @@ export const updateProfileHandler = async ({ ctx, input }: UpdateProfileOptions)
           emailFrom: user.email,
           // We know email has been changed here so we can use input
 
-          emailTo: input.email!,
+          emailTo: input.email ?? "",
         },
       });
     }
diff --git a/packages/trpc/server/routers/viewer/ooo/outOfOfficeCreateOrUpdate.handler.ts b/packages/trpc/server/routers/viewer/ooo/outOfOfficeCreateOrUpdate.handler.ts
index cb3b8c8616..b33795e6e4 100644
--- a/packages/trpc/server/routers/viewer/ooo/outOfOfficeCreateOrUpdate.handler.ts
+++ b/packages/trpc/server/routers/viewer/ooo/outOfOfficeCreateOrUpdate.handler.ts
@@ -45,7 +45,7 @@ export const outOfOfficeCreateOrUpdate = async ({ ctx, input }: TBookingRedirect
   let oooUserOrgId = ctx.user.organizationId;
   let oooUserFullName = ctx.user.name;
 
-  let isAdmin;
+  let isAdmin: boolean | undefined;
   if (input.forUserId) {
     isAdmin = await isAdminForUser(ctx.user.id, input.forUserId);
     if (!isAdmin) {
diff --git a/packages/trpc/server/routers/viewer/organizations/listMembers.handler.ts b/packages/trpc/server/routers/viewer/organizations/listMembers.handler.ts
index 4722897677..5fc210c0b3 100644
--- a/packages/trpc/server/routers/viewer/organizations/listMembers.handler.ts
+++ b/packages/trpc/server/routers/viewer/organizations/listMembers.handler.ts
@@ -283,7 +283,17 @@ export const listMembersHandler = async ({ ctx, input }: GetOptions) => {
   const members = await Promise.all(
     teamMembers?.map(async (membership) => {
       const user = await new UserRepository(prisma).enrichUserWithItsProfile({ user: membership.user });
-      let attributes;
+      let attributes:
+        | Array<{
+            id: string;
+            value: string;
+            slug: string;
+            attributeId: string;
+            weight: number;
+            isGroup: boolean;
+            contains: string[];
+          }>
+        | undefined;
 
       if (expand?.includes("attributes")) {
         attributes = await prisma.attributeToUser
diff --git a/packages/trpc/server/routers/viewer/slots/util.ts b/packages/trpc/server/routers/viewer/slots/util.ts
index b66a1bffa5..775043eaa9 100644
--- a/packages/trpc/server/routers/viewer/slots/util.ts
+++ b/packages/trpc/server/routers/viewer/slots/util.ts
@@ -381,8 +381,8 @@ export class AvailableSlotsService {
   }) {
     if (!eventTypeSlug || !slug) return null;
 
-    let teamId;
-    let userId;
+    let teamId: number | undefined;
+    let userId: number | undefined;
     if (isTeamEvent) {
       teamId = await this.getTeamIdFromSlug(
         slug,
@@ -1307,7 +1307,7 @@ export class AvailableSlotsService {
 
         const restrictionTimezone = eventType.useBookerTimezone
           ? input.timeZone
-          : restrictionSchedule.timeZone!;
+          : restrictionSchedule.timeZone ?? "UTC";
         const eventLength = input.duration || eventType.length;
 
         const restrictionAvailability = restrictionSchedule.availability.map((rule) => ({
diff --git a/packages/trpc/server/routers/viewer/teams/resendInvitation.handler.ts b/packages/trpc/server/routers/viewer/teams/resendInvitation.handler.ts
index 216f99a7a2..96e85aac5c 100644
--- a/packages/trpc/server/routers/viewer/teams/resendInvitation.handler.ts
+++ b/packages/trpc/server/routers/viewer/teams/resendInvitation.handler.ts
@@ -27,7 +27,7 @@ export const resendInvitationHandler = async ({ ctx, input }: InviteMemberOption
     isOrg: input.isOrg,
   });
 
-  let verificationToken;
+  let verificationToken: Awaited<ReturnType<typeof VerificationTokenRepository.updateTeamInviteTokenExpirationDate>> | undefined;
 
   try {
     verificationToken = await VerificationTokenRepository.updateTeamInviteTokenExpirationDate({