My banking app didn't work for a while on Graphene OS, but now it does again. In the interim I was able to use the bank's mobile website in a pinch. Password manager apps (I've tried Bitwarden and KeePassDX) integrate with the hardened Vanadium browser and made signing in a breeze. I lost immediate transaction notifications, but it was at least tolerable.

I suspect banks won't ever be able to take their web portals down and go app-only, though Google is now trying to ram through technologies in the Chrome browser to "verify the computing platform" that will have a similar effect to the Google Play "integrity" checks for apps.

Enduring solutions to these vendor lock-in efforts must ultimately be legislative.