Gender is determined at conception
Sex, not gender. Gender means 'culturally bound stereotypes about the sexes'.... people confuse the two leading to all sorts of muddled ideas....
It is impossible to change sex. Stereotypes about men and women can and do change over the years....
There have always been people who wanted to socially live as the other sex and mostly they haven't really caused many problems. But now a bunch of medical hucksters are telling people it's possible to physically change sex (it's not) and those who in the past would just be heterosexual transvestites (another common enough minority) have found a way to force the rest of society to play along with their kink....