Even 4chan removes child sexual abuse material at lightening speed. There isn't any major social media site that allows this. If it's even more now, would you be able to name an account that shares such stuff? Or are we supposed to believe this without evidence?
And as far as porn goes sure. The thing about Twitter is you wouldn't see porn unless you specifically go and look for it. Which is why I always find it amusing when people complain about this "problem". There is no porn in people's feeds by default, one has to train the algo to show it by searching for it and interacting with porn accounts. It's especially funny since on Twitter itself there are always conservative or Christian accounts complaining to Musk that they see too much adult content and that he needs to ban it.