That's because the itch.io PC version is currently unsupported. The devs said they're looking into changing that, but haven't promised anything or given a timeframe. If Steam isn't a problem for you, the download page here has a Steam key you can use. Otherwise, contact itch.io support to get a refund, and if you still want the game, consider picking it up on Epic or playing the mobile version if you have a phone that can run it.