Shoot, sorry about that! Did some googling, looks like this can be an issue for Mac Mojave. Let me know if this doesn’t work: https://answers.unity.com/questions/1377896/the-application-cant-be-opened-mac-build-problem.html
I got the same error in Catalina (10.15.5), but the Unity post fixed it:
chmod a+x AnAfternoonRippling_Mac.app/Contents/MacOS/*
afterwards though, I got 'developer couldn't be verified' and had to go into security&privacy panel, General, and unlock, start game, and allow 'open anyway'.
