Comment by Cider9986

It would be accurate to call it official support if it means they have set up their app with the privacy-friendly Android Hardware Attestation API on GrapheneOS.

Unless I'm wrong and they just support Basic Play Integrity or a lower one, I don't know much about that. But those would require play services. I could test to see if it works without play services which would indicate they are using the Hardware Attestation API to check the bootloader lock.