Oh she is 100% reading, viewing hentai (anime porn), and possibly writing about male homosexual sex. If she continues, genderwoowoo is her future. She needs to be off the internet and interacting with actual human beings again. Finding activities away from screens if you can might help.

Insight-this was me. Me and my friend group loved anime, and the stuff geared towards that age group was sexual even back then. I can't believe I was allowed to watch/read some of it (and what I got my hands on anyway was nothing short of graphic pornography), and 15 years ago the internet was not as accessible so the fact I had to purchase most of my stuff should let you know she has access to much more hardcore materials than we did back then. And why? Because yaoi is written by women for women as idealized male relationships. The boys around her suck, and fake ones are better - at least how most of us felt. And of course they were! They were a woman's fantasy. As an adult, I still enjoy some anime but stay far away from the 'community' because it's predatory as fuck. Hell, a lot of anime is predatory and there are loopholes exploited by artists to involve actual pedophilia.

And it's probably against the grain here- but I say let her pretend as long as there is no medical intervention. If I were to speak for myself, I'd say she's probably just wanting to dress 'masculine' because being a female 11 year old is uncomfortable and her female anime role models tend to be sexualized. She might even want to cosplay male characters because she likes them better or they have better (less revealing) costumes.

So, back to your problem. If it were me and you have the ability, I'd enroll with her in martial arts, Jui Jitsu, MMA just something where she can go and learn to feel strong in her body and be away from screens and she could pretend she was training to be a ninja instead of a boy. Or a sewing/ art class so she can make her own costumes/comics. The sex convo will probably make her run in the other direction, but a gentle reminder that her posts may attract attention she is not ready for because of the way she is portraying herself. Let her know you know she is going to post, you can't control it but you want her to be mindful of her content (and that men are disgusting-don't post any photos ever). When social media started becoming mainstream, a question my hs teachers would ask is 'is what you are posting something you would want me or an employer to see?". Remind her that everything she puts on the internet can be traced back to her, and that it does follow you (shout-out to the former cam models trying to get jobs-I hear it's tough when your boss can find pictures of your privates). And if she starts being defensive, you found her content. It stands to reason that others can as well.

And if you need to go hardcore, and I mean last resort, print her posts and post them around your parent's house. If she is confident in what she is saying, she should have no problem with Mom and Dad seeing it all. Then get her therapy.