The answer to this, like most identity-related questions, vary pretty significantly by the individual.
Some people transition because they feel more comfortable presenting in ways stereotypical of the other gender, others because they feel dysphoric with their body. Most are some combination of both.
Personally, I don’t feel much “social” dysphoria as I am (mostly) comfortable with my presentation, however I feel pretty intense body dysphoria, so my transition was primarily physical, with some lifestyle changes to fit in better.
It’s possible that dismantling of binary gender norms may allow more people to live comfortably without feeling the need to transition, but when you really deconstruct that argument, it’s not really useful. What matters is the reality of people’s experiences. In practice, that argument is usually used to discredit trans experiences as “made-up”.
It’s akin to saying, “People wouldn’t wear clothes (weather permitting) if we dismantled stigma around nudity.” Some people, maybe—it depends on the situation. Pragmatically, we live in a world where it matters, so it’s not a useful argument.
Regarding sexuality, there’s a significant lack of statistical data. There was some progress being made, but recent stigma has slowed scientific research into the topic. Personally I don’t think sexually can ever be fully decoupled from gender as a sense of self is often a significant part of sexuality. That being said, sometimes people change orientation when transitioning, sometimes they don’t. A combination of changing hormones and improved self-image can make a big difference in sexuality.
Uh oh, it sounds like they want us to be inclusive of all cars.