When trying to open an image with a custom editor, there is no warning message when launching the editor fails. For instance, I had Preview registered as editor, but since Catalina the actual path of the application is now /System/Applications and no longer just /Applications launching Preview as editor was not working, but PM did not warn me about this at all which made me wonder what was going on.
The same issue regularly crops up with Photoshop since they (annoyingly) rename the app about every year.
It would be nice if PM would warn about the launch failure.