Social media may really be harming teenagers even though the studies find almost nothing, because everyone is exposed and the studies compare harmed children with harmed children.

I think it’s entirely plausible that screens have a real negative effect on teenagers, but studies can’t find them because (a) the effects need not be dose-dependent (maybe two hours on your phone isn’t worse than one hour), and (b) given that everyone else is on social media, giving it up can have a negative effect.