My workaround for using both NFC payments and Graphene OS is wearing a Google Pixel Watch (1). All other Google Wallet features besides NFC payments should work.

[1] https://discuss.grapheneos.org/d/475-wallet-google-pay/4

Sadly that solution does not work everywhere. In a lot of countries, Google Pay cards are added by the bank's app and it's on the bank to support rolling out cards on WearOS as well. A lot of banks in my country only support putting a card in Wallet on phones, but not WearOS watches (not sure if it is laziness on their part or whether security of WearOS watches is not deemed acceptable in general due to the lack of secure elements, shorter/no PINs, etc.).