Looks like with iOS 14.2 Apple have changed the signature format used for code signing of iOS applications.
Starting in iOS 14.2 beta 2, the system checks for a new, more secure signature format. A user that launches an app signed with the old format receives a warning that the app must be re-signed using the new format. In a future release, the new format will become mandatory, and the system won’t launch apps with the old signature format.
If you are signing iOS applications yourself as part of the development process or resigning iOS applications for distribution you need to ensure that the Mac used for code signature is running macOS 10.14 or later.
You can check if the application is code signed correctly by running
codesign -dv /path/to/MyApp.app
You can resign the application by either using the built in command tools or iOS app resigning tool
iOS App Signer - Instructions (dantheman827.github.io)
Apple documentation on this:
Using the Latest Code Signature Format | Apple Developer Documentation
Apple have also sent notifications to developers that have applications in the store with outdated signature format
When a user launches an app on iOS 14.2 or later or iPadOS 14.2 or later, the device checks for a new, more secure signature format. One or more of your apps signed with your enterprise certificate still uses a legacy signature, which will cause the system to show an alert on launch explaining that your app won’t work with future OS versions.
To resolve this issue, re-sign your app on a Mac running macOS Catalina or later. In a future iOS and iPadOS release, apps with legacy signatures will no longer launch.
[Learn about using the latest code signature format.]( Apple Developer Documentation)
If you have any questions, contact us
Apple Developer Relations