Hmm, this error message actually sounds a bit like there could be something wrong on your end (absolutely not sure though!). The game files come as a .zip archive, maybe for some reason you can't open them directly on your end (I always thought this would work on Mac...). Have you tried extracting the downloaded .zip (by double-clicking it in Finder, I think) and then run the extracted file?
Oh, okay, didn't know that :)
I just think it sounds a bit strange that the operating system wants to open an app using the browser (but this could very well be perfectly normal, I'm not a Mac user). Is there something equivalent to the Windows "Right click -> Open with..." action on Mac? Maybe at some point something got mixed up and apps like this are supposed to be opened using a different program? Just shooting in the dark here, the most likely explanation is still a problem with the game engine Unity.
Sure no problem! I think the problem indeed lays in the fact that MacOS can't find a file format or program to execute to start the game. I'll keep you updated if I find the solution.
Keep me also updated if you find a solution. This could let a lot of games run on MacOS that now seem incompatible, despite having a Mac build.
I actually got it working, but it isn't plug and play!
Step 1: Open terminal
Step 2: type chmod +x
Step 3: Drag the file you find in: "Left click on the game -> Show package contents -> MacOS" to the terminal and press ''enter''.
(!) Dont't use ''enter'' between the chmod +x command and the file you want to drag.
This will make the file an executable file, which makes it possible to boot up the game.
The problem is that the Mac doesn't recognise the executable file on default.