In the paper: Sex beyond the genitalia: The human brain mosaic the authors state "Our results demonstrate that regardless of the cause of observed sex/gender differences in brain and behavior (nature or nurture), human brains cannot be categorized into two distinct classes: male brain/female brain."

This lead to a lot of media attention and articles repeating the claim.

However, this paper "Joel et al.'s method systematically fails to detect large, consistent sex differences" shows that the original study was significantly flawed.

Difference between male and female brains undermines the 'everything is socialisation' narrative which underpins things like 'toxic masculinity'.