"this tells us nothing about how many more men should be in STEM"

Why do you think that there is a right answer in the first place, to the question, "How many more men should be in STEM?"

What experiment could possibly test the effective working  hypothesis of those who agonise about gender gaps, that there should be equal numbers of men and women in every group?  Even to the point of using discrimination in order to produce equal numbers artificially?