Trying to wrap my head around 2FA... Any help?

Thanks! That confirmed and clarified what I had been reading. Thanks!

Also, particular app you recommend? They all kinda seem pretty much the same, lol. I would use it in conjunction with Gnome Authenticator on my laptop, so…

This one seems recently updated enough?

f-droid.org

Aegis Authenticator | F-Droid - Free and Open Source Android App Repository

Free, secure and open source 2FA app to manage tokens for your online services