Anything that requires "strong" hardware integrity attestation using the Play Integrity API will fail because Google won't add GrapheneOS and GrapheneOS won't spoof it.

So Google wallet /Google pay won't work. There may be other tap-to-pay apps that I'm not aware of that either use Android's Integrity API or only require the weaker attestation that's supported by GrapheneOS.

Same reason for all the other stuff I mentioned in my previous comment.