Passkeys do not work on GrapheneOS. I tested several sites and all of them failed.
One of them showed a error log:
Error: registration failed: android-safetynet attestation: ctsProfileMatch: the device is not compatible
I have Sandboxed Play Services and the Play Store installed.
Since Passkeys are the future and better than Passwords, is there a way around Play Services / a own implementation of Graphene?