Thanks everyone for the commentary. You can see my update to the post. This is not true, and `login.gov` still supports an authentication app as a second-factor.
The dialog in question is only for recovering your password, which is also an important flow to safeguard. In those cases it makes sense to use a different 2FA mechanism, so that you still have two separate factors for recovering your password. An authentication app was not an option in this dialog because it was already one of my factors.
I assumed that "Personal Key" was an authentication app, specifically in contrast to a "Security Key", and that I had to replace my 2FA option for regular logins with a different option.
The dialog in question is only for recovering your password, which is also an important flow to safeguard. In those cases it makes sense to use a different 2FA mechanism, so that you still have two separate factors for recovering your password. An authentication app was not an option in this dialog because it was already one of my factors.
I assumed that "Personal Key" was an authentication app, specifically in contrast to a "Security Key", and that I had to replace my 2FA option for regular logins with a different option.