That's not a "crackpot theory" but what the data currently show. This doesn't mean that there's a biological cause for this (although it's possible). But with IQ data, there's abundant evidence that the averages are similar, but men have greater variability:

https://pubmed.ncbi.nlm.nih.gov/26158978/

https://www.independent.co.uk/news/education/higher/dr-paul-...