I think it just means you gotta download from the website and not the desktop app bc it's not an application the desktop app can install. Log into your account through a browser and then go to your owned games, and then dl from there.
the reason why it says "no compatible upload" is bc it's like "hey bud, i can't install any of these files like an exe (or whatever mac and linux use to install), so uhhhhhh you're outta luck" and even though we're just trying to dl it normally, it won't do that. just desktop app things i guess lol