Here’s a crowd-sourced list of international banking apps that are compatible with GrapheneOS:
https://privsec.dev/posts/android/banking-applications-compatibility-with-grapheneos/

The issue tracker has slightly more current banking app reports:
https://github.com/PrivSec-dev/banking-apps-compat-report

Some banking apps may be problematic and here are some possible workaround solutions:
https://discuss.grapheneos.org/d/8330-app-compatibility-with-grapheneos