We can’t risk assessment every situation. But I would like to know what exactly the risk is to woman? In terms of statistics? I assume since you’re adamant it’s a big risk to woman, that there’s lots of evidence to back it up?
We segregate these kinds of places by sex, because it is recognised that men (as a class) are a risk to women, given that 98% of sexual offences are carried out by men. We don't risk assess every situation, we make blanket decisions which reduce risk. Which means that lots of men who are absolutely no threat to women whatsoever are not allowed into women's spaces. And everyone is generally fine with that.
We don't need to provide evidence that men are a risk, it's already there. And if you are saying that transwomen are not a risk, then the onus is on you to explain exactly why that is, given that they belong to the sex class which carries out the vast majority of sexual crime.