Where are you getting this message? The game should be playable on Windows, as it was made in Game Maker Studio 2. However, it isn’t currently playable on Mac, because a Mac OS computer is unfortunately required to export for the platform even if you own a license to do so. (I’ve considered borrowing or purchasing a laptop to export later builds, so Mac users don’t despair.)
I have been using the itch.io app on desktop (in Windows 10). I prefer the desktop app over the browser site since installing games from the app keeps it all nice and tidy in a hidden folder instead of cluttering the downloads/desktop.
I wonder if it's an issue with certain file types--shortly after I made the original comment ,I was looking at a friend's game that also showed this message in the app, even though it was definitely a Windows-compatible executable. Now that I am looking at your game on the web browser, it lets me download it just fine.
This seems to be a stupid bug that I encountered with some other games as well. Kiana, that is the reason why I made my post here some months ago. The problem still exists, the itch app says "not available".