To me, the whole issue of dresses is a huge red herring. It comes down to what we really mean by "gender non-conforming" I think and to a large degree that dovetails into some of the trans stuff, which is why so many parents who hate "gendered" clothing on young kids get sucked into gender ideology.
No one, gender non-conforming or not, has some desperate internal need to wear a dress to be authentic. That's just not part of our hardwear. There were neither cave girls nor cave boys who felt incomplete due to lack of dresses or gendered clothing more generally.
There absolutely can be interest, or preference, for a particular type of clothes, but that typically comes from two directions. One is that there is some comfort of practicality element. And I would say that where that is the case, often you see more flexibility in the customs in our society. A child of any sex can wear a jogging suit in public, and even look cool doing it.
The other is more an aesthetic attraction. With younger kids especially that can be imaginative mainly, but even grown ups can appreciate a certain look. But most people, even kids past about age 8 or so, don't generally feel that as some kind of obsessive need to wear a particular item of clothing. Most people also learn over time that clothes cut for the other sex often don't look aesthetically the same on the opposite sex - this is particularly true of dresses. And also that you can enjoy an aesthetic without necessarily having to wear it yourself. And finally, that many people enjoy several different looks, or on the other hand some are just indifferent to fashion all together.
It's normal for children to go through stages of understanding that there are customs around things like clothes, and then how these really fit into life. Often they go through stages of rigidity or over-generalizing, but they grow out of it.
All of which is to say that most people don't get so fixated on something like wearing dresses, and if they do i think it's pretty doubtful that it's about some kind of internal thing called gender non-conformity that inherently makes them only want to wear certain clothes associated with the opposite sex. It's about something else, and that won't be fixed by squashing all customs around clothing.
I think this is why the gender clinic in Toronto, before it shut down, focused on helping children become less fixated. Not because it was trying to make them "conform" but because the fixation was the real issue, not the dolls or dresses or whatever.