LSAG is a good shout but I’m not sure it’s sufficient. It enables anonymous verification of something against a set of known public keys. But you still need to make sure that set of public keys is coming from real humans. It’s not proof that a user has a property (i.e. being human), it’s just proof they are a user.
But yes this is sort of a digression from the actual main problem. The real anti-bot solution is a mix of methods imo.



GrapheneOS has some very strict requirements which basically means they will refuse to support anything except Pixel phones. Fairphone isn’t in the business of making their own (security) chips so I doubt the Graphene team will ever consider them.
CalyxOS, arguably the next best thing, did have support for earlier Fairphones but that project is sort of in limbo now.