Been trying to find the right kind of Sans content that steers clear of the adult stuff, but honestly? It's a real needle in a haystack. Most places just get flooded with everything, and the tagging systems on sites like AO3 are a total mess—people mis-tag stuff all the time, sometimes on purpose, so you'll click on something tagged 'no smut' and bam, it's not that at all. My best luck came from really old forums, like the ones from the peak Undertale fandom days, where writers were more about the alternative universe concepts and funny dialogue than anything else. You have to dig through pages of archives, though, which feels like archaeology at this point. I think the fandom's general vibe has just shifted over time, and the quieter, gen-fic crowd isn't as loud or centralized anymore.
I'd say if you're determined, maybe look for writers who are known for their Tumblr posts or have personal blogs where they host their own stories; they often have better control over their content and can explicitly state what they do and don't write. Otherwise, you're stuck sifting.