Ah I was about to ask what you meant with your post on the Steam discussion post. The Itch game page does have the following though:
Please note this game is in Early Access - most features are missing and bugs are to be expected. Check out the development roadmap to see upcoming features. As a thank you to early adopters, this early Itch.io edition will include a Steam key once King under the Mountain launches on Steam. You'll also be getting the cheapest price as the cost will increase once the game is ready to launch on Steam
I could add it to the download instructions as well if you think that would help. My current plan is to push a lot of updates/announcements when the Steam keys are available here though.