App quits right after launching

Since iOS 14, more and more users experience a severe problem: When they launch our app, it quits right after showing the launch screen, obviously even before executing one line of code.
In some cases, offloading and re-loading the app can help in this situation, but not always. In iOS 13, the problem occurred in the same way, but offloading and re-loading always helped.
This seems to be a licence problem and reinstalling is no option, because our app holds critical personal data that the user often did not backup. So what can we do in this situation?