It may help to post screenshot of your incoming server settings pane to get possible feedback. deleting the profile is not necessary as that contains your addressbook and other settings. However, to locate your profile, click help>troubleshootinginformation, scroll down to 'profile folder' and click 'open folder'. I share that for your information, not as a suggestion to delete it.

Thanks David. Screenshot attached of settings.

For profile, the open folder prompt doesn't work. It gives an error. Also attached.

Dan

Is the account authorized for IMAP? That is a requirement and can be set online with Gmail. My inference from your other screenshot is that you installed thunderbird from microsoft. I highly recommend that you uninnstall that version and install from https://www.thunderbird.net/en-US/thunderbird/all/ and pick there whether you want the ESR (128) or the monthly (138) versions.. Click help>about to see what you are currently using and decide as desired.

I've uninstalled previous version and reinstalled new version of Thunderbird. I deleted all profiles.

I can install some Gmail accounts but not others. Specifically I try to add one and it says error right off the bat. I don't even get the opportunity to add Oauth. It's just not there. It has IMAP enabled.

I recently changed my password for this Gmail account. Yet the new password doesn't work in Thunderbird. The old one does but it only has old emails! This is strange to me. How can I just get Thunderbird to sync with the new password for the Gmail account?

Please post a screenshot of thunderbird at the point where the error appears. That may help. Also, check that you have set thunderbird to accept cookies at settings>privacy&security. If you changed the password for an account already defined to Thunderbird, it may help to remove the existing passwords first at settings?privacy and security: - click savedpasswords and then showpasswords and then highlight both rows and delete them, - OR, just delete the account and add it back. What you're experiencing is that thunderbird is sending the old app password and it's being rejected.