Hey silvercenturian, are you using the Itch App? I bought the game 3 years ago and I can download the 1.0 Beta normally via my browser, but I can't install it via the Itch App.
That's likely because the dev forgot to flag the file as the installation file for Windows/Android OS. Note how other games usually show a little OS-specific symbol to the right of the file name. If the dev doesn't flag that correctly, the Itch App doesn't allow you to install the file.