Literally nobody does this
Just because a person identifies them as x, doesn't automatically mean other people have to be forced to accept them the same way. Just have a separate section for trans people in high school, separate for biological women etc.
The whole point of women's sports is arbitrary, and just as much as people should respect the freedom of a person to identify themselves as whatever they want to, the same people should respect the arbitrary rules of women's sports.
The issue is the people who want the world to be forced to accommodate them without consent.
As for a separate league for trans women... there are frequently like a couple dozen trans women athletes in an entire state. How exactly will that work for a separate league?
Except people clearly fucking do for some reason, and all that's going to happen is make life worse for women both cis and trans. Trans women will get excluded, and cis women who are "too good" or not fitting societal ideals of femininity will be accused of being trans. This is already happening to children.
> If you chose to identify as another sex
When did you choose to identify as the gender you were born with?
If you chose to identify as another sex, you can accept to give up on competing at the highest of the highest level. It's not like a big sacrifice.