GrapheneOS implements its own attestation so you can attest that it's real GrapheneOS. The valid approach they've chosen is to try and get on a level playing field with the big guys rather than destroy the playing field. They have a good argument their OS is very secure, so you should accept its attestation. This is how a user-friendly OS backdoors into the attestation system.

I still think destroying the playing field is better, but less likely to succeed.