Another juicy threat vector is forcing the app stores to stealthily ship a modified version of the app that sends copies of the IDs and/or tracking data to US intelligence services.

(Reminder: we know Persona's verification software already shares verification data with the federal government. It's a leap to modifying other apps, but within the realm of possibility of US government power. There is absolutely desire from them to gather blackmail material on politically important people, and age verification systems connected to adult sites/apps are a great way to do it)

This is a problem, but not the only one. The biggest one is that the phones in question are locked and deny user freedom. I would not be content with an European "alternative", but which is as locked as iOS.