It's not that complex, actually. There is no reason for a male category of athletics and, really, there hasn't traditionally been a male category. The NFL, NBA, NHL, and MLB are all open to anyone who can get hired by a team. These are (or, in the case of high school and college sport, should be) open categories. Anyone can compete in these categories, including women and girls.
The female category is the protected division. Only women and girls are (or should be) permitted to compete in the female category.
That doesn't mean you can't have other protected categories. That's what the para Olympics are, for example. Or even the special Olympics. The special Olympics aren't there because people with down syndrome aren't permitted to participate in the regular Olympics. They exists to allow people with mental challenges to compete on a more level playing field with others who have similar challenges.
It's not at all complex to say that Trans people should be able to compete either with one another or, when that opportunity is unavailable, to compete in the open category that is generally dominated by men. And then we save the women's category for women who were born women.