I think it's just the Itch.io app. Many different games have this problem. I've run into many games that have 1 of 2 errors: either a 3rd party error if the download uses mega or a similar site or a no compatible files. The latter is more rare. It's just because of the file type compatibility of the launcher through the app. I've found that if you just go to Itch.io on the web you can manually download it from there.