Contactless payments already work on GrapheneOS via Curve Pay, PayPal and the apps of many European banks. Solving the duopoly between Apple and Google for smartphone tap-to-pay in the US isn't something GrapheneOS can do.
Regulators / legislators can force Google to let GrapheneOS pass the Play Integrity API checks and Google Pay will start working.
>Contactless payments already work on GrapheneOS via Curve Pay
Are you sure about this? It was my understanding that NFC passes for gyms and stuff worked, but that if you want to pay for something with Google or Curve, you're shit outta luck