Here's the paper: https://epi.org.uk/wp-content/uploads/2021/01/EPI-PT_Young-p... It's all correlational (observing that people with higher social media use are worse off in various ways). This approach is not capable of detecting reverse causation (people use social media more because they are unhappy) or third causes (something else causes people to both use more social media and also be unhappy)
> “Those who feel worse may turn to social media for solace or community,” Dr Amy Orben, research fellow at Emmanuel College, University of Cambridge, said of the research.
“It’s not a vacuum, it works both ways."
But the actual article headline is the typical clickbait interpretation of a scientific study.