I probably would’ve taken the same position as you at one stage but now (over 20 years of parenting experience, 1 son, 2 daughters, 3 sets of parent-friends - one for each kid - all of whose other children, male and female I have witnessed growing up) I do believe there are tangible differences between the sexes almost from birth.
we are mammals, after all, and sexual dimorphism is a thing.
However, it’s a bell curve thingy and so there is a lot of overlap, and all children are unique so there is absolutely no reason to confine individuals to pink or blue boxes painted with the broad brush of sex stereotypes.
Sex differences exist but that doesn’t mean boys are better than girls.
The idea that boys and girls were exactly the same and it’s all just nurture/socialisation was an important concept for achieving work based rights for women but it’s also had the unfortunate side effect of ‘girls would be just as strong/fast as boys if they had better training/more money invested in their sports divisions’ and that’s just not true.
As an example, the reasoning behind ‘men should not hit women’ isn’t benevolent sexism, it’s because on average men are bigger and stronger and more likely to inflict serious damage on a female body than if the same man were to hit a male body with exactly the same force (see all the stats re women being injured in car crashes as an illustrator).
The reason we need single sex spaces and services and sex based rights in the workplace is because we are a sexually dimorphic species and that isn’t going to change.