Jonathan Haidt, who's been driving a lot of the work against social media for kids, directly refutes these findings in this post https://www.afterbabel.com/p/fundamental-flaws-part-3 .
The If Books Could Kill podcast did a good episode about this topic and Haidt's book in particular: https://www.buzzsprout.com/2040953/episodes/15546366-the-anx... >
The summary is this:
The uptick is adequately explained by changes to mandatory reporting requirements for screening questions of mental health for teenagers from Obamacare and increased access to healthcare for those teenagers.