Can't add Gmail to Mail.app in Catalina

I've seen this issue brought up, but none of the solutions worked for me and all previous threads seem to be locked. In Catalina, I had Gmail working just fine because I upgraded from Mojave and all settings came over. Suddently, my Gmail account wouldn't sync and it hasn't synced for 3 days. Tried all the standard stuff suggested here: Disabled / re-enabled account, Removed account completely from Mail, etc.

After deleting the Gmail account entirely from Mail.app, I tried to re-add it. Mail.app will open Safari so that you can authenticate with Google:

That step works. You sign-in with Google, you give your password. I've done it *with* and *without* 2nd factor auth turned on. In both cases, after you sign in with Google, literally nothing happens. The sigh-in screen disappears, and nothing happens. When you go back into Mail.app, the Gmail account is not there, and nothing has been added.

I opened a ticket with Apple Support and they had no further suggestions on this.

This definitley feels like a bug. Would appreciate your help and feedback!