It’s much easier to simply separate athletic competition based on gender. It can be assumed that a biological male will have been exposed to significant levels of testosterone.
Given the possibility that a pre-pubescent biological male may have T blocked medicinally or surgically they will never have been exposed to T and should be OK to compete with girls...they have no advantage.
Biological girls in transition will likely have been administered T and thus should be barred from competing with girls who are at a disadvantage because their natural T level is extremely low..coming from the Adrenal gland or from conversion of estrogens in the liver.
Make exposure to T the factor that governs whether or not an individual can compete with girls fairly.
There is a rather rare condition, complete androgen insensitivity. Those that have it, both male and female, are totally immune to the effects of T. The genetic girls who have it are ultra-feminine and the genetic boys are also..these boys cannot develop any male secondary characteristics and generally cannot pass as male at all.
Without the effects of T, which is an extremely powerful substance, both genetic sexes present as equals when it comes to athletic prowess.