I’ve had no issues personally with my banking apps. Most require sandboxes gPlay to be installed but there was no need to be logged into google for them.
Not sure now up to date this list is now but check out this site: https://privsec.dev/posts/android/banking-applications-compatibility-with-grapheneos/
I’m not fully up to date when it comes to e/os as I haven’t used it before. I believe it would be more private than the default os on fairphone considering google has been stripped out. I’d recommend doing research on the security updates of e/os, as if I’m not mistaken, these can often be significantly behind leaving you vulnerable.
If security updates aren’t quickly implemented, as I think they’re not - I wouldn’t recommended using it.