I remember watching hours of TV as a child in the 80s. I remember my cousins, born in the 90s staring like zombies at Cartoon Network when they were toddlers. We're all reasonably functional adults (most high achievers academically, and holding down well-paid jobs, with families). We also had huge amounts of screen time playing games, mostly on PCs.

If screens per-se are the problem, we'd have seen the same issues manifesting decades ago.

I think phones are the issue, rather than screens, specifically social media and notifications in particular. Someone suggested turning notifications off for social media, and it was a big change in my life, and something I've urged my own children to do as well.