https://itch.io/docs/creators/quality-guidelines#avoid-only-uploading-keys-or-li...
That's actually not really wanted on Itch. It is grounds for delisting and for refunds. Imagine what happens if you do not have a Steam account, and do not want or are not able to make one and accidentaly buy the game, because it is listed as a game. Itch is not a key shop.