F0RCE
I can't deeply test the functionality, but will look for obvious clues.
This got some steps to try if you haven't already:
https://discuss.grapheneos.org/d/8330-app-compatibility-with-grapheneos
And here is a small (WIP) collection, mostly from this support forum of things that may or may not disrupt functionality of some banking apps;
Location not enabled, or fake location detected
Developer options enabled
Adb used
Shizuku or rooting detected
Having a private space
More than one profile running
App installed in secondary user
App not installed from Play Store
Using a less common keyboard app
Screen sharing detected
Having no sim
System time out of sync
Very short system uptime
Vpn detected
Proxy usage
Private DNS enabled
GrapheneOS:
GrapheneOS not updated
Sandboxed Google Play Services not installed
Sandboxed Google Play Services not allowed running unrestricted
Sandboxed Google Play Services not allowed phone permission
Sandboxed Google Play Services not allowed network permission
Automatic exploit protection compatibility mode turned off