Installed grapheneOS on my pixel (finally) the other day. Actually was loving stock, until it got corrupted due to a bug. Had to factory reset to boot up again. Anyway, used that opportunity to install GOS.
NGL I do miss adaptive features and now playing, but I am liking GOS more and more day by day. Better battery life despite not having adaptive features, more security options like sensor permission and scopes, auto reboot if not unlocked feature and all that.
I use GPay and my bank app on a secondary profile. works seamlessly. Some UI improvements and adaptive features and it will be on par with the stock pixel experience itself.
You can create multiple user profiles in which you can install different apps. Each profile behaves as an independent phone installation in a way. That allows you to install google services to a specific user profile (with all the GrapheneOS sandboxing, controlling all permissions). Once you have google services, you can install google services dependent apps which basically work as they would normally.
There are some few banking apps which depend on something called “native code debugging” (a security feature). Normally it is advised to disable it for security but some banking apps need it enabled to be able to self inspect and verify integrity, from what I understand.
Edit: you can read more about GOS user profiles here: https://grapheneos.org/features#improved-user-profiles