Cannot enter second factor when Drupal in offline mode

Thanks for reporting this. I would say, this should be fixed by the main TFA module, so marking this as Won't fix here. There is already an issue in the TFA module, which is RTBC, so we need to get in touch with the maintainer, to get it reviewed/committed.

🐛 Maintenance mode blocks TOTP TFA entry Fixed

For those facing this challenge and are locked out of their Drupal, these steps allow you to temporarily log in your Drupal without any patch and without hacking Drupal at https://www.drupal.org/project/tfa/issues/2694723#comment-15216337 🐛 Maintenance mode blocks TOTP TFA entry Fixed