Connecting to a Gmail account in Thunderbird

I've been using Thunderbird to handle my email accounts for a long time (years). My Gmail connection was misbehaving, so I deleted the account on Thunderbird, verified that everything was still there by using the google.com/gmail interface (which works fine), then tried to recreate (reconnect) the Gmail account in Thunderbird. Followed the routine "Set Up Another Account", "Email", entered a name, gmail address, and password, then "Continue". Thunderbird looks up a configuration, finds Gmail, and it all looks normal. Checking in "Configure manually", OAuth2 is there. Click "Done", and it begins "Checking password", and never comes back......... I know the Gmail account and password are valid, because I can get mail directly from Google..... I'm at a loss...any suggestions would be appreciated.