HowTo: Disable or [Re]Enable Outlook Cached Mode (ie Emails not Sync'ing)
1. Click File > Account Settings > Account Settings
2. Select (Highlight) your email address > click Change
3. Under Offline Settings, uncheck Use Cached Exchange Mode to download email to an Outlook data file)
4. Exit (Close), then Restart (Re-Launch) Outlook
From <https://support.microsoft.com/en-us/office/turn-on-cached-exchange-mode-7885af08-9a60-4ec3-850a-e221c1ed0c1c#:~:text=Turn%20on%20or%20off%20Cached,Cached%20Exchange%20Mode%20check%20box>