Since the full text is only available behind a paywall it's difficult to make any substantive comment except that there sure is a lot of grant money available to study this topic. The lack of any conclusive or strong evidence given the multiplicity of the same studies over and over suggests if there is an effect it is weak at best. Also notable is that most studies pre-2019 on childrens mental health were fairly positive and most post 2019 negative. I can think of a lot of things that changed in 2019 but use of "social media" is not one of them.