Jonathan Haidt has done a ton of research on this and it's terrifying. His thesis seems to make a lot of sense: boys bully each other physically while girls bully each other reputationally. This is likely why mental health issues for boys and girls have diverged wildly since about 2014, because as lives moved online, this was a recipe for disaster for girls since social media is so perfect for this kind of bullying, but sort of a non-event for boys who were already online playing video games all day. Social media unlocked and turbocharged all those preexisting pathologies for girls.