I've recently switched to GrapheneOS, and I had issues using my old banks app (DNB, Norwegian bank) but my current bank (Sparebank1, also Norwegian) works perfectly on GrapheneOS.

I've also discovered that some apps that require safetynet, can be grabbed from the Huawei store and used, because apparently on chinese phones your bank suddenly doesn't need safetynet to be secure.

I do without issues, but it varies on your bank's app. There's a good chance you'll need Google Play Services, so you can receive two factor push notifications for example. But thankfully GrapheneOS has the option for Google Play Services to be installed sandboxed to varying degrees.