"New definition"?

Oh my sweet summer child, just because you're hearing about it only now doesn't mean this difference in sex and gender is new.

No, no, no.

It's older than the written word,

https://en.m.wikipedia.org/wiki/Third_gender#History

In Mesopotamian mythology, among the earliest written records of humanity, there are references to types of people who are not men and not women.

Also, you don't seem to understand the scientific side of the biological effects of HRT.

No, transitioning doesn't change your DNA. No-one has argued it does. This doesn't even remotely mean trans women are men or trans men women, and to make the argument that XY-people are all men or XX-people all women is to literally deny science, like a Flat Earther.