No one knows for sure, but if I take the perspective of a socially alienated young person who is angry, resentful, and feels a growing desire for revenge, I would say hours of screen time, social media dynamics [1], and widespread economic insecurities only worsen the situation. It is easy to become resentful and aggressive when you are isolated and feel left behind. Additionally, it is much easier to become radicalized as an isolated individual online. I believe that in the last century, it was more difficult to become radicalized from your own bedroom, and people had more social interactions, even if they weren't actively seeking them out.

[1] Anxiety surges in GenZ around its introduction: https://jonathanhaidt.com/social-media/

I suspect the copycat effect is a large part of it: https://en.wikipedia.org/wiki/Mass_shooting_contagion

The media has historically, starting with Columbine, been extremely irresponsible when it comes to school shootings, showing little of the discretion that it does when it comes to youth suicide (for which they've adopted professional standards informed by CDC, WHO, etc. recommendations: https://afsp.org/ethicalreporting/), to the point that it's given perpetrators fame that's endured decades after their demise: https://www.nytimes.com/2018/05/30/us/school-shootings-colum...

And they're doing this not just out of recklessness, but out of a pretty clear bias and desire to leverage these events to produce support for gun control.

Without any research I'd wager mental health among teens and young adults is very bad.

They don't really have a future. At least not a fun one to look forward to.