Somewhat. To fill out my taxes online, I could sign up with either the AGOV app (needs Google Android) or a USB security key. I happened to have a yubikey, but I needed to mess with the firefox about:config (security.webauth.u2f=true IIRC). It did work in the end though.

Yes. Without any issues still.

Gladly.

There was a time window 2 years ago where it appeared that I need an actual phone number to do my taxes, but even that was replaced with something more universal.