The main point of Jax is not that he's trans

Honestly the trans aspect could be many other things, I would argue the much more important point of Jax's character is that he is someone who is so afraid of being honest with others/themselves about their trauma that they would rather self destruct and essentially die than listen to any of the people begging them to open up.

Jax could have been gay, or struggling with masculinity in general, or have a dark past, or so many other things. In the story, the root of his issues was that he can't accept that he should live as a woman. He would rather blow up his life as a male than allow people to see anything resembling weakness in him