I just hit deploy for mac OS and it's not that they got an in-game error but they straight up couldn't open the file when they clicked on it.
Because you handled the deployment wrong.
If you deploy to MacOS from Windows, you'll get a folder, not a file. But that folder is the app under MacOS.
If you change anything on that folder before transfering to MacOS (like zipping it) that will NOT create an App under MacOS, but a zipped folder instead - and the Mac-User would have to rework that zipping or whatever you do before he can get the app to work.
But if you upload that to a website that expects to get an MacOS-App, that will never work.
The problem here is that MacOS hides the folder and pretends toward the user that it is an app based on a flag that does not exist in the Windows file system. So you need to copy the deployed folder to a MacOS, and set the flag that this folder is an app under MacOS before it can be uploaded to a website like gamespot or so on.