Thunderbird suddenly not connecting to gmail imap / setting up new gmail fails

As of a few days ago, I have the latest thunderbird installed and can't say when this began happening, but despite it working for years with two gmail accounts, neither gmail account will now sync / connect and it has authorization issues. I've then tried running thunderbird in a sandbox / uninstalling / reinstalling / deleting the user profile / registry entries, you name it...when setting up a gmail account in thunderbird, an error of "Authentication error. Unable to log in at server. Probably wrong configuration, username or password." come up, despite the password being verified as correct. If I manually setup gmail using the gmail settings, of imap.gmail.com / port 993 and SSL / TLS and Oauth2, and do a test, I'm met with "Connection to server.imap.gmail.com:993 failed" Nothing has changed on my computer in the time leading up to this not working. No windows updates performed...no changes to the firewall etc. You name it. I've checked it all. Strange! Any ideas? Thanks!