Specifically, the research that went into the book The Anxious Generation.
"O most expert Theuth, one man can give birth to the elements of an art, but only another can judge how they can benefit or harm those who will use them. And now, since you are the father of writing, your affection for it has made you describe its effects as the opposite of what they really are. In fact, it will introduce forgetfulness into the soul of those who learn it: they will not practice using their memory because they will put their trust in writing, which is external and depends on signs that belong to others, instead of trying to remember from the inside, completely on their own."
I'm sure there are different stressors and challenges on young people that I didn't experience at their age, but "what's wrong with" is immediately the wrong framing. It flies in the face of a history of human adaptation to their environment. The notion that the newest batch of challenges is different, fundamentally, from previous ones is the kind of thinking that leads people to hold up THESE ARE THE END TIMES signs in the streets generation after generation for thousands of years.
(Having a couple teenagers in my life: the challenges they experience are special and different from what I experienced, but mine were different from my parents and their parents lived through one or two world wars).
When I was a kid I had Saturday morning cartoons, but was bored a lot. Video games existed, but you got bored of those fast and rarely got new ones. We went outside a lot. Kids these days (as well as adults) have access to 24/7 dopamine hits. That doesn't mean we're in the end times, but I don't think humans were meant to live in our own curated digital bubbles. People are now less used to socializing in person and it seems to be causing exacerbated feelings of loneliness and depression.
Of course my father complained whenever I wasn't hard at work, but the difference seems to be the magnitude of the modern problem. At times I think humanity is rapidly evolving into something else and the physical bodies we have can't keep up. I can't imagine the next thousand years of progress.
What I'll be surprised by is if kids can survive the black death and the second World War and not a smartphone in their pocket.
It is entirely possible that without equivalent biological change, the attack upon the human spirit by various forms of media will become critical and at some point the kids really will not be alright.
We've seen too many generations asking that question for me to conclude that there is anything wrong with them. There's just a lot of ways to be human, and they're exploring a different channel than my generation did.