If so, how did it go? If not, what is the legal hangup that would make such a suit unsuccessful?
You say that it's "widely accepted that social media causes depression". Are there any studies in the peer-reviewed scientific literature that have shown this? Are there any studies that have shown it's false? If this ever went to trial, each side would have to bring expert witnesses to testify to these conflicting claims, and a jury would need to decide which side was more credible.
Also, a plaintiff who claimed that social media or gaming caused their depression would have to prove that this was actually the case. How would they prove that their condition wasn't caused by something else in their life (or just by genetic predisposition) and that their addiction to social media wasn't just a symptom of their condition? Will your psychiatrist testify to this on your behalf? (Don't have a psychiatrist? So how do you know that you're actually suffering from depression?)
Finally, chances are that most of the members of the jury will be social media users who enjoy it or at least don't consider their lives to have been damaged by it. You'll have to convince them that something that they do every day without ill effects has somehow harmed you.