Here is the best I can do:
"if Steam keys are free to me as the developer when/if Nox Archaist is released on Steam, I will provide you a steam key at no cost if you purchase the game on itch.io"
The main hedge in there is the "when/if" because I have never donea Steam release, so I don't know what I don't know. I've read their FAQ and it looks like a $100 fee and a bunch of work setting stuff up and that doesn't concern me....but you never know when you will find devils in the details.
I appreciate your interest!