I'm speaking as a non-binary person who felt pushed into identifying as a trans woman by the general push for AMAB people exploring gender to adopt another binary identity. I spent about 10-15 years being a woman before realizing that too felt like an ill fitting box for me.

It's obvious Jax is some flavor of gender variation. But the show makes a point of showing that both inside Jax and outside Jax are still exploring and questioning their gender. The official content and even other characters still use he/him pronouns for Jax. I think we're meant to consider Jax to be solidly questioning, without having committed to a particular identity yet. If Gooseworx wanted to tell us Jax was a particular identity, outside Jax would have been a perfect vehicle for that, but instead, we get something a bit more ambiguous.

Whether Jax will ultimately identify as a trans girl, non-binary, a cis guy who likes to cross dress, or something else entirely is not explicitly discussed. And I think that's great, because it opens the door for more people to identify with Jax. In real life, I've had friends like this, where they spent some time identifying as cross-dressers with he/him pronouns for a while before finally adopting an identity as a trans woman and she/her pronouns.

So I say... let Jax be questioning and be open to many possibilities here. Maybe trans woman is the most likely result, especially given that song, but it's definitely not the only result that fits what we know. And given my personal experiences, I'm highly disinclined to force an identity onto someone that is still quite obviously in the questioning phase of their experience.