I actually couldn't get it to run as a native app on mac, but installing & launching through the itch desktop app did the trick (as others have pointed out). Go to itch's home page, then click "download app" if you don't have it already. It sort of behaves like a launcher / manager for your itch games, similar to the steam one.
(I'm not entirely sure WHY this works, I tried a while to get the normal download & run of the game to work but failed)