https://www.cdc.gov/nchs/products/databriefs/db513.htm#Key_finding Important note:
During July 2021 through December 2023, one-half of teenagers ages 12–17 had 4 hours or more of daily screen time (50.4%).
I wouldn’t be surprised to find teenagers depressed and anxious during a pandemic.
Furthermore it is clear that this study only confirms correlation.
It’s definitely more complicated than that. Based on things I have read, social media helps some neurodivergent kids who have trouble making friends in school have a social life. It’s easier for some of them to have friends when they don’t have to worry about things like interpreting their emotions from their facial expressions.
I think likely screen time reduces anxiety and depression for those teens because it lets them do something that avoids such things due to lack of friendships.
Good point about correlation, entirety possible the depressed and anxious people may tend to increase screen use.