Telegram does have E2EE, just not in regular chats. Its secret chats are E2EE, as are its voice and video calls.
I also think it has the best UI of any of the messengers, personally. It’s customizable and very polished overall, at least on Android. Very smooth/optimized while having loads of features and lots of little animations to make things flow nicely without getting in the way.
I do like Signal and Matrix clients as well, though I just wish Matrix had more of a user base.
Nudity isn’t inherently sexual, and they pointedly have not mentioned it in the quoted text. It sounds like only explicit sexual content is forbidden, not nudity.
I do think even this is an overreach for a federated network, though, assuming Pixelfed is enforcing this on all instances (is that even possible?). It should be on the instance owners to make that decision. I couldn’t find where the quoted text is sourced from, however.