"Google requires completing authentication in your web browser."
In my Apple Mail 13.4 and OS 10.15.7 the above message keeps popping up for my Gmail account.
I saw on the forum that there are 11 posts with exactly the same problem.
No logical answer or fix to be found.
When going in System Preferences -> Internet Accounts -> My Gmail account, there is nowhere the Password to be filled in/corrected/or changed.
The pop up window that supposed to lead to the "Google Authentication" offers only Safari, but when clicking on it, it disappears and nothing happens.
MacBook Air 13″, macOS 10.15