No idea. But it does not sound like a Thunderbird issue if another account with the same provider using the same settings in the same profile is working.

Perhaps share the troubleshooting information on the help menu (copy to clipboard and paste in)

I've tried EVERYTHING! TB will not accept a second gmail account. As mentioned, the settings are the same as the first account and all seem well until I click 'DONE' then I get "unable to log in at server". All settings are entered by TB but at the last step are rejected. This problem started with the new version.

This is a sceenshot of the error from TB when setting up a second Gmail account.

checking password should pop up a web page from Google advising you to enter your credentials and authorize Thunderbird to access that account.

Failure of that process is rather has some well known causes. They are mostly documented here https://support.mozilla.org/en-US/kb/automatic-conversion-google-mail-accounts-oauth20

Additionally if there is some other software monitoring the local host the process will fail to save the oauth settings.

What you are suggesting is that the process is not even starting. This sounds more like an external product is blocking the HTTPS request. So I would be looking for security software being over helpful. Perhaps a software firewall blocking web page requests from Thunderbird as it is not your "browser"

You can log the account wizard process, but I rather doubt it will be all that helpful. But it certainly can not hurt. My attempt to explain how to do that is here https://thunderbirdtweaks.blogspot.com/2021/10/logging-new-account-wizard.html