Men as a group produce sperm, women as a group produce ova. And intersex people are male or female with disorders of sexual development. Two sexes because reproduction.
The human being has two arms, it’s not a spectrum from 0 to 3. If you are born without arms or with an extra arm, human beings still have 2 arms, regardless of your abnormality. If you amputate your arms you are still human, if you attach an arm, stillhuman.
Let’s not pretend biological sex is so complex that some males are women based on their wishes. A transwoman is a transwoman, they cannot expected to be treated as the opposite-sex when it comes to sex-segregated spaces, though they can, of course, live life as they imagine it to be for women, helped along by people forced to pretend they are the opposite sex lest their self-conceptions are invalidated by reality. The demands of trans activists have become absurd and require a denial of reality and re-definition of “man” or “woman” to such a degree that these terms are meaningless. Now we have gender non-binary people claiming there are no bathrooms meeting their metaphysical needs…go use the bathroom designed for your biology, it’s not hard.