My Gmail POP and SMTP stopped working today as well. I updated to Thunderbird 91 and changed the `Authentication method` to OAuth2 and that fixed the problem for me. I don't know if IMAP requires any other changes or not.

It is fixed now. I tried later to change from "Normal Password" to OAuth2 and the server accepted it and then went through the authorization process. I believe that Google made the OAuth2 authentication mandatory before they were ready to accept it.

Similar problem: Google's 2F2 Gmail authentication is set up to send me a text when logging in through a 'less secure app' -AKA Thunderbird. Windows 10 environment. Thunderbird (imap) email server settings are set to SSL/TLS and OAuth2. I'm updated to the latest version (As of Oct 1'22). When trying to log in, T-bird delivers an 'authentication error' message. I'm simply not receiving the 2F2 authentication code from Google when trying to login via T-Bird.

FYI: My second account -Enterprize version from work- is set up exactly the same and there I do get the F2F authentication shunt to sign in via work, and then use Thunderbird no problem. But not in my basic/home/personal account.

[This whole 'less secure app' access crap has been going on for years. Seriously, Mozilla & Google have to sort this out. I'm a die-hard Thunderbird user, but this is frustrating.]