Microsoft 365 for MAC OS

To fix a Microsoft 365 activation loop on a Mac, you can use the Microsoft License Removal Tool to clear conflicting credentials, or follow these common solutions:

Remove Old License Files (Keychain & Removal Tool)

Conflicting or cached old license files on macOS frequently cause Office to loop the activation prompt. 

• Open Spotlight Search (Cmd + Space), type Keychain Access, and open the app.

• Type Office in the keychain search box and delete any saved Office license or token entries.
• Download and run the official License Removal Tool for Mac to delete persistence files.
• Restart your Mac.

Check Your Microsoft Account Sign-In

• Open any Office app like Word.
• Click Word in the top-left menu bar and select About Word -> More Info… -> Refresh License (if available).
• Completely sign out of the app, close it, reopen it, and sign back in using the exact email address tied to your active Microsoft 365 subscription. Make sure you aren't signed into a conflicting old school, work, or expired personal account.

Clear Group Container Files

• Quit all Office applications.
• Open Finder, press Cmd + Shift + G, and go to /Library/Group Containers/.
• Locate and delete the contents of these folders:
  • UBF8346G9.ms
  • UBF8T346G9.Office
• Restart your Mac and launch Word to sign in again.

Remove Duplicate or Old Office Apps

• Check your /Applications folder.
• If older versions (like Office 2019 or 2021) are still installed alongside Microsoft 365, they will conflict. Move old Office apps to the Trash, empty the Trash, and restar

You might try your question on the Microsoft Forums:

https://learn.microsoft.com/en-us/answers/tags/831/m365-office  

Just to clarify, you do have a Microsoft 365 subscription, correct?

There is an elegant alternative—

Free and private office suite, no forced AI — LibreOffice

Did you obtain MS 365 from Microsoft or a Microsoft reseller (e.g. Amazon), or from the Apple App Store? The answers will be different depending on how you obtained MS 365.