Uhhhhh, why is it trying to install something? It's just an HTML file.
I just tested downloading and running the file and it worked fine for me.
"No mapping for file extension HTML" makes it sound like whatever you're using to download the game doesn't know what an HTML file is (is that the official Itch program, or something?), I'd probably recommend downloading the game normally and opening it in a web browser by hand, I don't know what that program's trying to do with the file, but it's not doing it correctly.