Don't give up just yet. I'm sure Steam and Itch will find workable solutions for this problem.
We may have to go back to what was done before NSFW content was explicitly allowed on Steam. Devs would censor their product, but the censorship could often be bypassed by "patching" the game (usually with an empty text file named "patch.txt" or something similar).
Don't let the pearl-clutchers and spreaders of moral panic discourage you. Your game is excellent and I'd hate to see it die because of this half-assed attempt at censorship.