Go to the preference of the application. Go to premmision there and tick the box saying acces as excitable file
It isn't so much that the installation script isn't configured properly as that there isn't an installation script. The game's just a basic executable file; it's intended to be downloaded and played normally. I'd like to support the itch app integration eventually, but I didn't even know about it until a few weeks after launch, so it's going to be a future thing.