Oh my, that has just been there the whole time and I repeatedly glossed over it!

Yeah, it’s generally my preferred method but for small things like this that I’m personally not having issues with I let it do the thing in the background.

I don't think you can as a user. The instance you're logged in to can defederate from the other instance but it's not something that you can do yourself AFAIK.

Yeah, it was about the same for me - so far no issues but I never ran in to the fingerprint issue either so I can't confirm whether or not it's resolved for me.

There was mention that the update was rolling out gradually to devices and different carriers, so there’s a good chance that it just hasn’t reached AT&T or your device just yet.