Put it this way.... Let This Be Your Last Battlefield is subtle compared to some of modern Trek.
One of the problems with writing ‘issue’ Trek, is its supposed to be in a utopian future where most of not all our ‘problems’ are already done and dealt with. So Trek typically uses alien races to talk about ‘now’ in the ‘future’. That way, you get the message in without offending the part of the audience the message is for.
Trans issues in a human race that has advanced medical technology like genetronic replicators, pills that grow kidneys, access to full on telepaths and empaths, and literally disassembles and reassembles people on the molecular level like we go to bathroom (but conversely has banned genetic engineering) makes zero sense. 100 percent changing biological sex *would* be possible in Trek, probably at any point in a humans life, and diagnosis is as easy a Betazoid meeting a person and going ‘yup’.
So that’s the in universe reason for needing allegory. There’s no need for intermediate ‘they’ stages in the process.
Out of universe, if you are trying to get through to an audience hostile to trans issues, then it’s no good rubbing their face in it, because that’s how you alienate the audience you are trying to reach. Spock has a *ton* of stuff to do with the difficulties of being ‘mixed-race’ and living as part of two cultures, at a time where acknowledging that is even a thing was tantamount to heresy. But, not once did the audience complain about that that I know of. And maybe, just maybe, when Johnny Appleseed the Fifth met their half-Vietnamese granddaughter a couple of years later, Spock helped that relationship.
