diff --git a/packages/app-store/office365calendar/lib/CalendarService.ts b/packages/app-store/office365calendar/lib/CalendarService.ts
index ba908b1a89..29bd859c76 100644
--- a/packages/app-store/office365calendar/lib/CalendarService.ts
+++ b/packages/app-store/office365calendar/lib/CalendarService.ts
@@ -1,5 +1,6 @@
 import type { Calendar as OfficeCalendar, User, Event } from "@microsoft/microsoft-graph-types-beta";
 import type { DefaultBodyType } from "msw";
+import { findIana } from "windows-iana";
 
 import { MSTeamsLocationType } from "@calcom/app-store/constants";
 import dayjs from "@calcom/dayjs";
@@ -688,20 +689,58 @@ export default class Office365CalendarService implements Calendar {
     return response.json();
   }
 
+  /**
+   * Gets the main timezone from Office365 mailbox settings.
+   * Handles both legacy string format and new Graph API object format due to API evolution.
+   * Legacy format: returns string timezone as-is (preserves existing behavior)
+   * New format: converts Windows timezone from {"value": "Windows Timezone"} to IANA format
+   */
   async getMainTimeZone(): Promise<string> {
     try {
       const response = await this.fetcher(`${await this.getUserEndpoint()}/mailboxSettings/timeZone`);
-      const timezone = await handleErrorsJson<string>(response);
+      const timezoneResponse = await handleErrorsJson<string | { value: string }>(response);
 
-      if (!timezone || typeof timezone !== "string") {
+      if (typeof timezoneResponse === "object" && timezoneResponse !== null && "value" in timezoneResponse) {
+        const windowsTimezoneName = timezoneResponse.value;
+        this.log.info("timezone found in outlook mailbox settings (new format)", {
+          windowsTimezoneName,
+        });
+
+        try {
+          const ianaTimezone = findIana(windowsTimezoneName);
+          if (ianaTimezone && ianaTimezone.length > 0) {
+            const convertedTimezone = ianaTimezone[0];
+            this.log.info("Successfully converted Windows timezone to IANA", {
+              windowsTimezoneName,
+              convertedTimezone,
+            });
+            return convertedTimezone;
+          } else {
+            this.log.warn("Could not convert Windows timezone to IANA, using original value", {
+              windowsTimezoneName,
+            });
+            return windowsTimezoneName;
+          }
+        } catch (conversionError) {
+          this.log.warn("Error converting Windows timezone to IANA, using original value", {
+            windowsTimezoneName,
+            conversionError,
+          });
+          return windowsTimezoneName;
+        }
+      }
+
+      if (!timezoneResponse || typeof timezoneResponse !== "string") {
         this.log.warn("No timezone found in outlook mailbox settings, defaulting to Europe/London", {
-          timezone,
+          timezoneResponse,
         });
         return "Europe/London";
       }
-      this.log.info("timezone found in outlook mailbox settings", { timezone });
 
-      return timezone;
+      this.log.info("timezone found in outlook mailbox settings (legacy format)", {
+        timezone: timezoneResponse,
+      });
+      return timezoneResponse;
     } catch (error) {
       this.log.error("Error getting main timezone from Office365 Calendar", { error });
       throw error;
diff --git a/packages/app-store/office365calendar/package.json b/packages/app-store/office365calendar/package.json
index 419c194fb1..098b32572e 100644
--- a/packages/app-store/office365calendar/package.json
+++ b/packages/app-store/office365calendar/package.json
@@ -8,7 +8,8 @@
   "dependencies": {
     "@calcom/lib": "workspace:*",
     "@calcom/prisma": "workspace:*",
-    "msw": "^2.7.0"
+    "msw": "^2.7.0",
+    "windows-iana": "^5.1.0"
   },
   "devDependencies": {
     "@calcom/types": "workspace:*"
diff --git a/packages/platform/examples/base/src/pages/_app.tsx b/packages/platform/examples/base/src/pages/_app.tsx
index d35433c584..2c78641a85 100644
--- a/packages/platform/examples/base/src/pages/_app.tsx
+++ b/packages/platform/examples/base/src/pages/_app.tsx
@@ -73,7 +73,7 @@ export default function App({ Component, pageProps }: AppProps) {
     }
   }, []);
   useEffect(() => {
-    if (!!selectedUser) {
+    if (selectedUser) {
       setAccessToken(selectedUser.accessToken);
       setUserEmail(selectedUser.email);
       setUsername(selectedUser.username);
@@ -83,13 +83,15 @@ export default function App({ Component, pageProps }: AppProps) {
   return (
     <div className={`${poppins.className} text-black`}>
       {options.length > 0 && (
-        <Select defaultValue={selectedUser} onChange={setSelectedUser} options={options} />
+        <Select
+          defaultValue={options.find((opt: TUser | null) => opt?.email.includes("lauris"))}
+          onChange={(opt: TUser | null) => setSelectedUser(opt)}
+          options={options}
+        />
       )}
       <CalProvider
         accessToken={accessToken}
-        // eslint-disable-next-line turbo/no-undeclared-env-vars
         clientId={process.env.NEXT_PUBLIC_X_CAL_ID ?? ""}
-        // eslint-disable-next-line turbo/no-undeclared-env-vars
         options={{ apiUrl: process.env.NEXT_PUBLIC_CALCOM_API_URL ?? "", refreshUrl: "/api/refresh" }}>
         {email ? (
           <>
diff --git a/yarn.lock b/yarn.lock
index ef0d1aaaad..18cc484d12 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3750,6 +3750,7 @@ __metadata:
     "@calcom/prisma": "workspace:*"
     "@calcom/types": "workspace:*"
     msw: ^2.7.0
+    windows-iana: ^5.1.0
   languageName: unknown
   linkType: soft
 
@@ -49166,6 +49167,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"windows-iana@npm:^5.1.0":
+  version: 5.1.0
+  resolution: "windows-iana@npm:5.1.0"
+  checksum: 0dc9ababde5f839e83a4bcd448347d8da563efd9e23ce61ac777e9992774ff85de2a9f343f87b80b37b181742fe4d783cff3ba39191cfedb6357ae7d5f58aadc
+  languageName: node
+  linkType: hard
+
 "winston-transport@npm:^4.5.0, winston-transport@npm:^4.9.0":
   version: 4.9.0
   resolution: "winston-transport@npm:4.9.0"