Apple forces developers to code sign an app using the latest code signature format and IPP needs to support it.
a related link:
[Link Removed]
1. Package a project to iOS on Windows
2. UBT compiles a project and codesign it natively with the latest code signature format.
3. In the packaging stage, IPP resigns IPA and changes its code signature to the old format. (0x20200)
4. Run the IPA on iOS 14.2 and above then see the compatibility warning.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-107274 in the post.