It is perfectly functional for any regular website. However that's not something we can just add to our itch.io page. It's a feature the devs of itch.io could enable for everyone. Perhaps its possible to detect mobiles and tablets from media queries in CSS, but that would only rely on the size of the screen which is way less reliable than this library. Another hacky way would be to integrate an iframe in the itch.io page to replace the download options by something external, which would integrate this script.
No I haven't try yet on itch.io but I use it on my regular website to warn mobile users that my game is only for PC.