strange, theres a few nsfw mods like buttplug.io support and big asses, though i have noticed that the one mod that added a canine dick isn't findable on thunderstore either, maybe they're against exlicit stuff like genitalia? anyway you're right I can't find rules anywhere on the site either (would be stupid if you can only see guidlines in a discord server or something, have you tried asking about that?)
Viewing post in FunnyBits [NSFW Webfishing Mod] comments
bigpants apparently existed before the rule was in place so they let it go because it wasn't really explicit anyways, though not sure why it seems like the buttplug mod has been able to slide.
either way i wouldn't wanna bother them about it, especially so long as i have somewhere to host the mod. hopefully someday the rules will get a page on the wiki or something, though.