The numbers ... support at the very least a flattening of growth. See "Americans’ Social Media Use 2025" <https://www.pewresearch.org/internet/2025/11/20/americans-so...>.

Note that that survey asks what social media U.S. adults ever use. Time on site, trending over years, would be more interesting to see, but I'm having trouble finding any recent research.

I have seen indications that Twitter is actively shedding both readers and time-on-site, and that Facebook/Meta numbers are strongly buoyed by purchases (WhatsApp, Instagram). Others I'm not so familiar with.