After using LineageOS for long time, I have finally moved to GrapheneOS. I use a lot of banking and financial apps which I never felt comfortable using on LineageOS due to lack of proper sandboxing, unlocked bootloader etc.
GrapheneOS works flawlessly just like Android. You don’t even notice there’s hardening underneath. Also it protects from Google’s evil location tracking using WiFi/Bluetooth or even when the Location is turned off. I don’t understand how people in general are comfortable with Google tracking all the time. You can use Google Play and Play Services in a sandbox that works just like regular installation, but without deep tracking.
If you haven’t tried GrapheneOS, try it. You won’t go back to regular Android.
Definitely go ahead and tell your bank that you are annoyed by their mobile app only working on the stock OS. Call them, send them an email, whatever. If enough people complain or even threaten to switch banks over this, they might add better support using actual secure hardware-based attestation, which also works on GrapheneOS.
I even switched banks because of their ridiculous requirements for the mobile app, just so I could continue using GrapheneOS. I know that Graphene is much more secure than any other Android-based OS, and running my banking app on it is much safer than on another device. Banks should finally realize this too, which is why we need to complain.