A person’s biological sex is on their birth certificate and cannot change. However a tiny minority of people want to present as and be accepted as a gender different from their biological sex. This is permitted by law. Some critics of this deny the idea of “gender”. They find the idea that biological sex can be different from adopted gender unacceptable. The law of the land disagrees.

(formerly Bruce Jenner)
When it comes to the oft-posed question “What is a woman ?” it seems that the answer is that it is identical to gender whether that conforms to biological sex or only to adopted gender . If a biological male chooses to present as a female-gendered person then he (a man biologically) becomes a woman legally.
If I’m right (tell me why I’m not under the law) then aren’t we making a mountain out of a molehill given the rarity of transitioning.
(To avoid doubt I strongly believe that women who have transitioned need to be exceptionally sensitive in all-women spaces (preferably avoid them) and that they should never compete in female sport.)