Jailbreak message on banking app

It may be. Did you ever try (or succeed) in downgrading your iOS on your iPhone? There is no Apple approved way of doing this and is referred to as "Jailbreaking" which voids all further warranty and support from Apple. For more info, see:

Unauthorized modification of iOS can cause security vulnerabilities, instability, shortened battery life, and other issues - Apple Support

If not, see the reply to:

iOS 14 Jailbroken warning message - Apple Community

SCAM! I assume your phone is not jailbroken. They are trying to get you to reveal important info. Delete and move on...

Either the app has not been updated to support the latest version of iOS or you jailbroke your device.

If you didn’t jailbreak, you will have to wait for them to update their app.

i should also mention this could be triggered by using a beta version of iOS.

Johnathan is probably right about this one. We saw a number of these issues recently.