*Edit: I had someone test Catalina with the itch.io desktop app and it seemed to run the game, so try that first!
OK, it seems that Catalina has trouble extracting zipped files properly, so other games are also having this problem. Currently the two solutions I've seen are to use the Unarchiver app or to use the Terminal to give the executable permissions back: https://itch.io/post/1516186
I tried to upload a noncompressed file to see if that would work, but itch doesn't allow you to upload folders, and my computer sees .app as a folder.
I hope this helps! I wish I could do something more to fix it.