You can bypass Play Store restrictions on app installs by using Aurora Store. There's a high chance your banking app can be used but it may require toggling the per-app exploit protection compatibility mode. Most banking apps work on GrapheneOS. X is one of extremely few apps disallowing using a non-Google-certified OS but it only partially disallows it in their store listing which can be worked around and for regular password login. Login is still possible to X via a passkey or Google login. X should stop doing that but they're quite understaffed and did this as a misguided anti-spam measure.
Aurora store is a horrible placeabo. Not only is it using other folks anonymized accounts, which violates several privacy laws internationally it also still has the Google libraries in their apks like everything else. You are not gaining any privacy or security using Aurora Store or F Droid for that matter but are indeed opening up more attack surface in the supply chain that ends at your device.