Replying to everyone who said to use Google Authenticator. I in fact did fall for the devious wording that implied no other Auth app would work but never fear, even that is not an option for my account now that I'm checking. The only available options are physical security keys (which I lack), phone numbers (which I won't disclose), and tapping a notification on an Android phone (which ties me even more into the Google ecosystem and I'd rather not pick). I'll appreciate any comments if anyone knows how to get a TOTP going with Authy for Gmail, don't assume I know everything and I'm willfully ignoring it!