The download does not start, it stops
Did a little bit of digging. This seems to be an issue on itch.io's end. Some people think it has something to do with the download getting interrupted and being unable to resume. A few possible workarounds I found online were to either stay on the download page while it downloads or to install it from the itch.io desktop app. Neither of those solutions seem very ideal, but unfortunately it doesn't seem like something I can fix on my side.