Same issue here...There is a link/key to another game on Itch for downloading, rather than the Steam key for this game.
Wonder if itch is having issues. There is still keys available and this is what it says in the back "Keys will be distributed to a purchaser when they first click the request key button on their purchase page."
On the purchase page where the button to request the key for Steam is not a key but just a link to another game of yours, namely Serenity's New Gig
Lg