Comment by ulrikrasmussen

There are viable third alternatives which do not require building a full smartphone stack. The national eID in Denmark, MitID, is an app "protected by" Play Integrity, but at least there are two non-smartphone alternatives available in the form of either a TOTP code generator or a FIDO2 chip which you can get for free if you can't or won't buy a smartphone.

Age verification solutions could also be built on dedicated hardware tokens, even though the tokens required to build a ZKP or blind signature based solution may not be available off the shelf right now.