because of mac os catalina being the worst thing ever, it doesn't like opening apps from unity that weren't made on a mac at this time, hope it gets fixed, i feel your pain
The problem is the app isn't executable. To fix this problem open Terminal and change directory "cd /Applications/floppy\ minecraft\ mac.app/Contents/MacOS" and make the file executable by using this command"chmod 755 ./not\ minecraft\ dont\ sue\ me\ pls".
