re :. I have removed the account from Thunderbird, as well as all the related contacts,

Oauth request access can occur for mail account email and gmail contact address book and also gmail calendars.

You say you have completely removed the gmail mail account. So it's no longer in Thunderbird. You mention removing all related contacts - however contacts are just email addresses which can be move to any address book.....can I assume you have also removed all gmail address books ?

Have you removed all gmail calendars that were related to the account?

Have you removed saved passwords for that gmail account?

• Settings > Privacy & Security
• Scroll down to 'Passwords' section
• Click on 'Saved Passwords'

If you see any lines that mention gmail and the email address of 'removed' gmail account, then select the relevant lines(s) and click on 'Remove'. Click on 'Close'

Exit/Close Thunderbird and wait a few moments for background processes to complete and then start Thunderbird.

Thanks for the reply. I had gone through all these steps and I have nothing left from this Workspace in any inbox or address book or passwords. That is why I'm at a loss. Google have obviously passed the buck for Thunderbird to resolve. I suppose I have to live with this Google dialog window popping up every 10 minutes....

If you are receiving login requests for an account that was removed, along with possibly a related address book or calendar, there is a way to eliminate the requests:

https://support.mozilla.org/en-US/questions/1525801

Thank you @sfhowes. I followed the suggestions regarding the prefs.js file, and there it was, lines still syncing to the disabled Google Workspace account. I removed the relevant lines and the pop-up requesting credentials is no longer coming up. This is very much appreciated. Celine.