There are quite a few threads on this board that cover the subject. Googling something like "Mumsnet autism gender" would probably bring up several.
From my own experience of working through it with my daughter, my thoughts on how autism and the questioning of gender identity overlap are as follows:
A resistance to change - your own body changing is the ultimate betrayal. How dare my body do this? It must need fixing.
Sensory - boobs feel weird in clothing. They get in the way. I don't need them.
Sensory - Periods are awful. What's the point in having them. I don't want children anyway.
Androgyny - Many autistic girls don't see any point in the impracticality of skirts, dresses, sequins, hair accessories etc. I like wearing "boys' clothes"
Anxiety/low self-esteem/being bullied for being a "weirdo".... and...
Social media combined with Be Kind - there is community out there that is calling me in. They don't bully me. They understand me and I can find my people here.
Exiting girlhood - girls are weak. If I was stronger I could stop those bullies.
Obsession/fixation/locked in thinking - There is an answer! I must be a boy! It is the only logical explanation. I'm not going to change my mind. I'm determined.
The bias in the medical and mental health professions - let's start by affirming your identity and take it one step at a time. Change your name, change your pronouns... Not feeling better yet? OK, let's bind your breasts. Still not feeling any better and your breasts are now getting bigger... OK, let's put you on puberty blockers to give you some time to think and pause your physical development before you feel any worse... Still no better? Have some hormones. Still no better and you've got back pain from all the binding...? Well, "top surgery" is your answer. Check out all these happy cool people who are posting photos of themselves with their surgery scars. Do you want to feel like that too? Instead of: let's explore why you're feeling at odds with your body.. and how that might link to your wider mental health issues and experiences.
We've found that sports bras and the mini-pill have been very helpful in reducing the stress associated with our daughter's changing body. They are not silver bullets and we're still working through some difficulties but they certainly help to slow the pace of the change resulting from puberty, to give her more chance to get accustomed to it all.