There's really nothing to do here, unfortunately.
If an app chooses to require a Google certified Android OS, GrapheneOS can't do anything about that. Any workarounds that can be done to spoof this will stop working permanently in the future.
Apps that use SafetyNet / Play Integrity API that want to allow GrapheneOS can do so by following this guide, however:
https://grapheneos.org/articles/attestation-compatibility-guide