so that means you have to buy it from steam
The itch.io version also comes with a Steam key. You can find it on your download page for the game. You don't need to repurchase the game. Doesn't help the growing numbers of users who are avoiding Steam,though. Which particularly sucks for those who are forced to do so because Valve turned their client into a health hazard for some people with migraines, epilepsy, vertigo and several other conditions and have knowingly refused to fix it for over 18 months now.