I've seen someone else mention Dr Az's book above, with a lot more detail than I did. Reading his book and/or listening to him speak (e.g. the interview with Andrew Gold) is a good way to digest his understanding of autism meets gender identity.
I appreciate that doesn't directly answer your question but I think it's really good to have as a foundation as, from what I've seen, Dr Az is much stronger in his knowledge of males with autism than females when it comes to this subject. He doesn't seem to have that much interest in females who identify as trans IMO. But his stuff is still helpful to unpick autism from gender identity.
Regarding conversations, I can only speak from my own experience but choice of words has been key. I needed my daughter to know I wasn't challenging her directly.
For example if I had said the TIF equivalent of this... but also let him know that the best you will be able to do is think of him as a man pretending to be a woman?.... that would have lit the touchpaper. The emotive word here would be "pretending" but the overall sentiment would have been received by my daughter as judging her and either the shutters would have come down... or the immediate anger would have kicked in.
Instead, I asked exploratory questions with open curiosity, mostly focusing on how she experienced her body rather than what she thought a man or a woman was. Things like "If I'm understanding it properly, you don't like your breasts. Is that right? <pause and listen> Is it the way they feel do you think?" <pause and listen>.
Also, I did lots of "I wonder....". That's a PDA (Pathological Demand Avoidance) technique which is used to reduce the feeling of demand... If something feels like a demand the likely response will be fight or flight - a perception that "I can't answer/do this because it's going to harm me, so I need to resist it and make sure I'm in control of the situation instead". Essentially, stubbornness on acid.
In "classic PDA" (nothing to do with gender identity) that could mean saying "I wonder if you're feeling sad" as an alternative to a direct question like "do you feel sad?" or "I wonder if we need to start putting our shoes on yet to get to the shop before it closes" as an alternative to "get your shoes on now please because the shop is closing".
Effectively, PDA techniques are about giving a feeling of control (because being out of control raises anxiety and increases the likelihood of a fight/flight response) within guardrails that are set by the parent. When I applied this to gender identity, the guardrails were that I wasn't going to let my daughter access anything that caused her harm (I told her this, explaining that this was part of my role as a parent) but I also promised her I would learn everything I could about gender identity, including by listening to people who were trans identified. I asked her if she thought that sounded fair and she said it did. I do appreciate that's easier with a 13 year old than someone older, but the principle could still work. It's a bit like making a "deal" where my daughter knew that I was actively checking in with her and, in many ways, "problem solving" together.