https://www.city-journal.org/understanding-the-sex-binary
I found this very clear. This is the conclusion.
^The “sex binary” refers to the biological reality that there are only two sexes—male and female—and that these categories refer to individuals whose primary sex organs are organized around the production of either sperm (male) or ova (female). The “sex binary” does not entail that every human is unambiguously either male or female, even though the vast majority are.
This is an important distinction, because adopting the second framing is inaccurate and plays into the hands of activists who seek to debunk the existence of only two sexes by calling attention to the existence of rare edge cases (i.e., “intersex” conditions). But the first framing (“there are only two sexes”) is both biologically accurate and ensures that two distinct concepts—transgenderism and intersex—remain distinct. It also puts to rest the false notion that the existence of rare edge cases necessarily entails that sex is a “spectrum” and that we are all therefore intersex to some degree.
Crafting effective policy therefore requires treating transgenderism and intersex as the distinct concepts that they are. It also requires not falling into activists’ trap of conflating intersex with transgender. An effective policy to prevent males in female spaces would be simply to require that “female” refer to one’s birth sex; sex chromosomes can be used as a backup when there is doubt. Intersex or DSD policies should prioritize safety and fairness, with specifics left to the individual organizations to decide.
While activists are insistent in presenting the biology of sex as being so complex as to defy all categorization, and categorization itself as a social evil, we should resist the urge to counter them by adopting their overly simplistic misrepresentations of the sex binary. We must not make the biology of sex more (or less) complex than it is.