7 Things You Should Know Before Switching to GrapheneOS
https://www.howtogeek.com/7-things-you-should-know-before-switching-to-graphene-os/
https://www.howtogeek.com/7-things-you-should-know-before-switching-to-graphene-os/
Mandated is the wrong word. "Required for absolutely everything" is more precise. In Denmark you need an app called "MitID" to do any kind of digital verification. You can't do online purchases, banking or digital bureaucracy without it.
You can use a keychain OTP generator (in Norway). I have no clue how it generates verifiable codes. The phone app is more convenient, and to the point at hand, actually connected to the internet/NFC. In any case it's factor 1 in a 2FA (And then some), so the same way any 2FA would work.