Impressive how little you know what you're talking about. And then you admit it while still so confidently stating that someone "can't" be who they are!
Sah (and Arin, their actor) is nonbinary but that doesn't mean they need to conform to any outer gender expression. They can choose to have visible breasts or not. In fact Arin had top surgery some time ago so Sah has never had breasts. Did you notice? Does that mean that Arin has to be a he/him? They're not!
It is complex but this complexity is not just a soap thing and I do recommend you read about it before commenting. Especially using the wrong pronouns for a character who has been more than clear that they use "they/them" and never, at all, "she/her".
In fact when Sah was first introduced there was a great deal of confusion in this thread about whether they were a boy or a girl. The answer "neither" was not good enough - people really needed to know both the character and the actor's birth sex. Absolutely none of anyone's business.
This thread is noticeably awful about Sah's identity when it's really not a difficult thing. Just use their name if you're not comfortable with they/them pronouns.
I'm a huge fan of Arin Smethurst as a nonbinary person on primetime BBC and Casualty is treating their story pretty sensitively, as Casualty goes. I wasn't hugely into how the show introduced their mother and made their deadname public knowledge, but haven't seen anyone being shitty about that as yet.
Nonbinary representation is such a good thing and it's so sad how a tiny minority make such a lot of noise about tearing it down.