There's generally rules of the "have to be on HRT for X months" kind which is perfectly sensible: Your body doesn't change the second you come out, or decide to swallow pills.
Then, all the data we have says that middling athletes stay middling after transitioning, bad ones stay bad and great ones stay great, that's enough for fairness given that we don't disqualify Michael Phelps for being half fish. All those genetic advantages he has would carry over if he were to transition and he'd dominate the female league not because he transitioned but because he's a genetic freak.
If you think that people transition just to have an advantage I don't know what to tell you either. I'll believe it when I see Matt Walsh do it, on camera, under doctor's supervision. If that clown with all his hatred can't do it with ideological fuel then noone can.