I wanted to add on here because I need some advice regarding my friend. She’s in her 20’s now and is also on the autism spectrum. we’ve been close since middle school. As you can probably assume, she now desires to troon out. A few months ago, she texted me saying how she wants to become a boy. She’s been going back and forth and just so confused and it honestly breaks my heart. She also hangs around some other pooners and there’s no doubt in my mind they’ve left an ugly mark on her. I care so much about her but I don’t want to say anything right now as I don’t want us to lose contact. I’m just scared she’ll start making rash decisions and eventually come to regret them. If you guys have any advice then I’d appreciate it, I’m really desperate.
You have to be honest with her, truly honest. Tell her you come from a place of concern, that you want to be there for her and, at the same time, you're worried this is a quick fix that doesn't address whatever problems she has going on in life. It's possible to still be friends with her even if she goes down this path, but many people have changed their entire persona in the course of following it. Don't react out of fear, really think it through, and consider if you might regret if you don't speak your mind honestly.
Don't think you can tell her how to live her life, don't try to lecture her, just be as candid as possible about how worried you are that this is a bad idea. Give your reasons, say that you'd love to be wrong about it, but you don't think you are. This isn't about convincing her not to troon out, precisely, but about helping her find the right path to happiness. Emphasize that you don't want this to blow up the friendship, that she's welcome to disagree with you, this isn't some ultimatum but you feeling a duty to speak your mind. The best kinds of friends will give each other the absolute truth; if you want to be kind of a joker about it, point out that that's peak male mentality and if she's truly a man she's understand.
Jokes aside, good luck. I don't want to say anything dramatic like "be willing to lose your friend", but you have to risk it if you want to voice your concerns. If she cuts you off over it, then it was just a matter of time.