See https://www.thunderbird.net/en-US/thunderbird/91.7.0/system-requirements/

Hi, Matt. I'm confused now. The 91.7.0 Systems Requirements only list MacOS 11, aka Big Sur, but not MacOS 12, aka Monterey. However, in this post from December Wayne Mery answered that Monterey is supported: https://support.mozilla.org/en-US/questions/1362066

 - Which answer is correct?
 - If Monterey is not supported yet then when is this planned?

Personally i would say if Wayne said it was supported, it is supported. He has been running the release testing for a number of years.

Basically new operating system versions are automatically supported as really little changes version to version. Mostly a new coat of paint over the old and creaking internals that have been getting polished for the last 20 years. There is also little new in windows 11, and it is also not on the supported list. But in both instances Thunderbird runs on the operating system. I think it is telling that Thunderbird operating system list is actually just copied from that of Firefox and the disk space requirement is actually so fictional that you can not install a 64 bit copy of Thunderbird and configure it in the space the web site says is the minimum.

But the important list of support and the one that really is the key is System Requirements: Details

   Windows: Windows 7 or later
   Mac: macOS 10.12 or later
   Linux: GTK+ 3.14 or higher

as it is operating systems being dropped that is more of interest than new ones not listed.

A reply to my own message - took me some time to find the solution - is to alter the alter the Authentication method to OAuth2. Then quit from Thunderbird and restart the app. Google will take over and as you to first log in and then to allow for Thunderbird to have access of which you allow. Then when Thunderbird commences, it finally works.