I'm unsure how many have enabled 2FA and use a password manager. However, logging in doesn't work well when you have a password manager. I have tried 1Password and the Safari password manager, and they both have the same problem. When you go to log in, the password manager fills in the username and password and submits the form, but then gets an error because the auth code wasn't filled.

Maybe updating the JS to not to error if the 2FA auth isn't filled in, but to keep the username and password filled in and then display the 2FA field so the password manager can fill that in.

Just a suggestion to make it a little easier. Not a big deal, though, because you don't need to log in very often.