so apparently this is a known problem on itchio
since i'm using godot 4, i have to enable an option (SharedArrayBuffer) in the project settings on itchio for the web version to work, but by doing so the download no longer works on some browsers (like firefox). if i disable this option, the download will work, but not the web version, which is the one i prefer to keep, so i have to leave the option activated
as far as i know, there are no solutions to this problem yet. however, the download should work on chrome or edge (as mentioned in my previous message). and on firefox, there's a way around the problem: copy the link of the blocked page and paste it in a new tab, the download should now work (at least on my side this works, but if it doesn't for you let me know)