all android devices have been using file based disk encryption since several Android versions now.

All Android devices are supposed to support it, but not all do. (or at least, not all do effectively without compromising the cryptographic root of trust by not implementing proper hardware security chips)

I’ll grant it to you on the scopes, PIN changes, etc, but realistically I just don’t think anyone can justify GrapheneOS being something that should be supported on Fairphone given how absolutely desolate the phone looks with regard to any attempt at all to hardware security.