I’m of the opinion nothing should be left untouched overall. Obviously it depends where you host or publish because everything will have their own rules for content.
But as for subject matter to avoid, like on principle? Nothing. I don’t consider anything to be too sensitive or touchy to have in any sort of media. It really just boils down to what you, individually, are sensitive too.
I, for example, am a-okay with rape, incest, bestiality (to an extent), necrophilia, and a myriad of other such dark subject matter.
However, I gag at the mere suggestion of polyamory. Far as I’m concerned I think it’s the worst and can’t stand the positive portrayals of it. It’s something that’s always been a hard no for me and that’s not going to change. I instantly drop anything that even implies it as a possibility and I never look back because the thought of it taints the entire thing.
So sure if I had it my way it wouldn’t be in any media ever but my point is that sensitive topics vary person to person. What you’re personally comfortable with, or are okay with exploring, is entirely up to the creator. So yeah I have personal limits but not in the “no comic should ever do this thing I don’t like” way.
That said I’m really into incest ships. Tho I’m pretty picky when it comes to them appearing in original works, I prefer it in the form of fanfic. Lol