Sorry, I meant to imply lightheartedness by including the word "joke". Must've been misplaced by me.
Anyway, the main takeaways of my previous comment were that:
1) Dividing the site's NSFW content of the pornographic variety and non-pornographic variety into categories would alleviate most of the issues surrounding it. As it currently is, a lot of crossover exists between the two due to how the tagging system fundamentally works.
2) Steam has a sub-par solution which only really proves that ultimately you'd need to make a separate site for it altogether. Since users are somehow able to label their games "adult-only" on there without either understanding what that means or due to the vagueness of the language itself.
Long story short. The structuring and language used to define what constitutes as adult are problematic and I think Itch.io and so forth have gotten a little too cozy with the site layouts to make any significant changes.