I cannot access to my mobile banking app as it says it’s not supported on jailbroken device. The thing is my iPhone is not jail broken. I contacted the bank and he said I need to check with Apple. May I know what’s wrong with Apple device?

The bank doesn't know what they're talking about. The bank needs to update their app to be compatible with the latest iOS versions. Most people at the bank probably wouldn't know this and it would be a question for the developers of the app. This will probably help - How to contact an app developer - Apple Support

He is passing the buck. This can only be fixed by the app developer.

Muyleng wrote:

I contacted the bank and he confirmed that the app is applicable for all regions. He insisted for me to contact Apple support.

You talked to an employee, not the developer and they don't know what they are talking about. Apple cannot fix this for you and will have to be taken care of by the developer.

This a bug, of sorts, that popped up with iOS 14. Some banks, for whatever reason, think your device is jailbroken when it isn't. Can't recall what the fix is, if there is one other than waiting for your bank to fix things on their end.

One of my financial institutions had this problem. I was able to still use the app after I dismissed the warning. Have you tried that?

The app was later updated and I now don't have to worry about it.

I just did a search online after you posted this and everything I find says it's up to the developer to fix it.