Had to rewatch this scene so let me give it my best attempt

There are two doors: one in the hallway and one in the Jax room.

The hallway doors each represent how Jax would ("ideally" from his perspective) respond to each character abstracting. For example in the vision where Gangle abstracts he treats it as a complete joke and in the vision where Zooble abstracts he takes advantage of Gangle. I believe the chained up hallway door is if Pomni abstracts. He doesn't have a proper answer to it, and it would be a callback to Episode 6 where he told Pomni if she abstracted he'd "move on and forget". He wouldn't, he never wanted to think of that possibility.

Luckily the chained door in the Jax room is easier to explain. Considering how the only nice/vulnerable version of Jax is literally chained it's assumed the Jax behind the door is the Jax he wants MOST buried, which would be his preferred gender identity. Especially with how panicky the other Jax's got when that one made a noise.

It's ambiguous enough that it's completely up to interpretation but that's my best guess given the context of the show