Perhaps reflecting some of the challenges in understanding the OSA, and also some of the technologies, there are some rather odd comments in the chat!
Specifically about fediverse services...
Discussion
Ofcom implictly making the point that it is for site admins in their content moderation role to make decisions about illegality.
As someone who has done this and who has done a little bit of reading about the law, this can be really quite tricky to get right.
So I suspect most sites will craft their terms, and their practices, and err on the side of caution.