As far as I know, there is no easy solution to this problem. However I have found most people who download games from itch on a mac know how to manually turn this off in the settings so it is not so much of a problem. Another, far worse problem you may run into which caused me a lot of trouble, is that when you build a game on a machine running windows of linux and create a MacOS build (I use Unity so not 100 percent sure that this problem carries over to other engines) then zip it up, the exec file loses its executable status on Mac. The user must enter the terminal and manually reinstate the .exec status for the file in order to launch the program. Here is a fix for that problem. I recommend putting a link to this in your download instruction for Mac users. Game won't open on Mac - Unity Forum