First, you should be using OAuth2 authentication when adding an IMAP gmail account (which is the default in the setup wizard), and use your normal account password. Second, you should have TB 60.9.1 or 68.2.1, which include a fix for google OAuth2 changes. An app password is only necessary if you use 'normal password' authentication, instead of OAuth2 (or use POP, which can't apply OAuth in TB).

http://kb.mozillazine.org/Using_Gmail_with_Thunderbird_and_Mozilla_Suite

Ah, I was running 60.8.0. I was certain I had just run an update earlier today, but I suppose not.

Once I updated I was able to log in successfully though, thank you!

I am running 60.9.0 and I don't see any location where I can get 60.9.1 - is that in any repository?

winickjr said

I am running 60.9.0 and I don't see any location where I can get 60.9.1 - is that in any repository?

If you're on Windows or OS X, 60.9.0 should update to 60.9.1 from Help/About TB. If you're on Linux and your distro hasn't released 60.9.1, there is a TB version. Or, you can apply the workaround in Edit/Preferences/Advanced/General/Config. editor.

I'm attempting to change my Gmail password and its original ones are SSL/TLS/OAuth2 authentication in Thunderbird v68.3.1. It can NOT work. Therefore I had removed and added it, but the result is same.

Boltnut said

I'm attempting to change my Gmail password and its original ones are SSL/TLS/OAuth2 authentication in Thunderbird v68.3.1. It can NOT work. Therefore I had removed and added it, but the result is same.

If you changed the password, make sure the old ones for imap:// and smtp:// are deleted from Options/Security/Passwords/Saved Passwords, then restart TB and enter the new one when adding the account. Also, check your TB version is 60.9.1 or 68.3.1.

Thanks. It can work now after removing the old one from Options/Security/Passwords/Saved Passwords.