Depends on the function. Bathroom are an entirely different test (penis/no penis). I think in sports where it matters, where there is undue influence caused by male puberty, where such influence cannot be corrected for and where there is sufficient mass, a third “open” category (open to all except xy men on testosterone, including ftm, mtf, intersex, hormonal imbalanced women, hormonal imbalanced men, nonbinary xx, and any xx that want to play) might be worth experimenting with. I agree there are only two genders…gender is not a spectrum…that said there are pegs which imperfectly fit into the 2 holes every once in a while.Then I go back to my argument to open up the third other gender category. It’s always been male and female for thousands of years. The neo liberals want to come and redefine reality to invent new sex genders outside of the natural binary gender that the Mammalian class naturally produces then recognize the other gender category in sports since trans numbers for this new generation are about 20% that equates to millions of trans now within that generation just in the USA alone. Why are they so quick to hide under the cisgender women umbrella? But they are so fast to identify as trans when its convenient