The devs have confirmed the itch.io PC version of the game is not being supported at present. They said they were going to look into this but have posted a roadmap since which makes no mention of it.
Some of us don't have Steam as an option (for various reasons), but if that isn't a problem for you, the download page for the game has a steam key you can redeem and that version should work.
And if that isn't an option, getting a refund is your next best choice. Not sure it'll be much better an option but the game is also on Epic now so after the refund you can probably re-purchase there.
And just to clarify: No, I don't think Epic is a good platform. It's awful. Still way less abusive than Valve has been in the past almost 2 yeears.