If that would really be the only option, don't make the app.

If it gets very popular, those who don't want to be tied to Google will be excluded from something important.

And the maker of this app thinks it could have a tremendous impact, so...

Maybe just trust the users, and rely on human moderation to deal with abuse. It's basically how any community works.

Standard AOSP Hardware Attestation.

Play Integrity passes for devices unpatched for several years, which makes it a joke.