Google Wallet works but tap-to-pay NFC payments don't because Google enforces strong Play Integrity for that portion. They only allow Google certified OSes to use it. It's a sad choice on their part, not GrapheneOS' fault or choice.
To me it's a biggest missing feature to date (and the team brought that up with European Commission already, as there are no technical or security reasons for that). Worth noting it will work on the old, unpatched, rooted, wildly unsafe phones with the right magisk configuration. But not on the safest os.
Anyway, it keeps the passes okay for me, and for the payments I use Garmin Pay.