Worldwide, the average person spends a total of 6 hours and 37 minutes looking at a screen each day (for internet-connected activities). The average American spends 7 hours looking at a screen each day. According to data from DataReportal, the average American spends 6 hours and 59 minutes looking at a screen every day.
www.crossrivertherapy.com

Are teenagers growing dimmer?

Every three years the oecd, a club mostly of rich countries, releases the results of international school tests sat by 15-year-olds all across the world. There were reasons to hope that the latest data, published on September 8th, would bring positive news. Marks in mathematics, reading and science had collapsed in the previous round of testing, which was carried out just after the pandemic.
www.economist.com

Screen time isn't the issue, you'd be a fool to propaganda to think its just screen time. The point of saying "screen time" is to put fear in people about computers, phones and its utility.

It's what they are doing with their screen time, over time they are doing less and less structured thinking.
A Short video, notifications, algorithmic feeds, constant task-switching, reduced long-form reading, less boredom, less unstructured thought.

It doesn't have to be this way its not screen time, but the apps they use.