Yes, what belonger said. If you are questioning this as a mother who has given birth, breastfed and obviously knows the reality of female reproductive organs, what maelstrom must this open up to young women who want to reject feminine stereotypes and wear/dress/present as they like.
There are three things and they should be kept separate.
Sex - sometimes called gender by people too polite to refer to genitals - your sex makes you female (otherwise no babies would have come out). This is a simple biological fact.
Gender - this is the way society expects men and women to act. So going back to the 1950s, the idea that women should aspire to motherhood, be nurturing and caring of the family home and this was the correct way for a woman to be, if she was herself properly brought up (see the psychiatric and psychoanalysis literature of the period for an explanation of this)
Gender - also used by second wave feminists to highlight and challenge that ideas of gender are malleable and change over time and place. Hence, whether you are a woman or man does not affect what you should wear, be paid, be allowed to do etc. (Note: Second Wave feminists made a distinction between gender and sex, in so far as also campaigned for abortion rights, same sex refuges and so on, because women seem to be oppressed on the basis of their sex; the third wave I think argued that gender is performative and cannot be disentangled neatly from sex, nonetheless the idea remained that gender is an external presentation of masculine/feminine)
Gender identity - comes also in the first instance from psychiatry, and is the innate understanding we are said to have from age two about whether we are male or female. But again, a distinction used to be made between sex identity (where dysphoria was an outcome) and gender identity, where the biggest problem (in 1950s psychiatry, specifically psychoanalysis, eyes, not mine) was not behaving in ways becoming to a woman.
My question about this is - the concept of gender identity was born in the late 1950s/early 1960s before the push for greater women’s rights and freedoms of the 1970s. Why has it gained currency again? And why has it gone from niche psychiatry to mainstream? And even in the 1950s, gender identity and sex identity (re dysphoria) were not the same thing. So the other stepping stone is queer theory, which breaks down established categories including sex, gender and sexuality, in the early 1990s which I think is what has led us into the current mess.
But even then, queer theory does not make sense as an explanation, because gender identity and the idea of being trans presupposes rigid categories one can transition from and to.
So in short, one can spend hours trying to work it out, but in reality we know that women, taking sex as the signifier, are the group of people who have historically and culturally been distinguished by virtue of having female reproductive organs and discriminated against by all the baggage that brings. Women can not identify out of greater rates of poverty due to caring responsibilities, they cannot identify out of rape, sexual abuse and sexual objectification, they cannot identify out of the physical damage of menstruation, menopause, endometriosis, prolapse. These are things we know - and can accept without being heteronormative or imposing feminine dress code and working/domestic patterns on women.
In short, one should be able to be a woman (sexed body), present as one wishes (masculine/feminine/why not do away with such concepts altogether) and not be questioned as to whether one IS male or female. What other great things could you being doing if your mind was not taken up by this?