This paper came out in October and I read it at the time. It is pretty surprising but it is also totally contradicted by other major surveys, so I am pretty sure it's just flawed. The most peculiar result is the dramatic reduction in reach for YouTube. This guy has YouTube with 60% reach and falling. Pew Americans’ Social Media Use 2025 has YouTube at 84% and rising, and 95% among 18-29 age cohort, which pretty much refutes this paper's core conclusion.

"Overall [social media] platform use slipped ... especially the youngest ... who no longer use social media at all" is the kind of wild claim that requires a much more significant investigation than this author undertook.