I’m not at all attuned to how young Japanese people discuss anything, but I remember reading some articles on a similar subject, and maybe swapping in 性自認 for 性別 would be a way to go?
Googling around to check if it’s plausible gives at least one usage of “あなたの性自認（自分の性の認識）は何ですか？” in a poll with lots of options, and curious if you could get away with talking about someone else’s 性自認, I tried “彼の性自認” and the results looked plausibly like the kind of discussions about a third party @TheMostPrizedPigeon was maybe asking about.
Take with a grain of salt though, I have zero experience talking to anyone in Japanese so offered only as potentially interesting speculation.