From what I’ve observed, people are increasingly checking out of social media (or turning their profiles private), because it’s just unappealing unless you’re actively promoting something.
What is also growing is the number of people signaling that they are out of it.
This is extra pernicious because the people that are staying in control of these environments are maintaining a large amount of leverage over everyone.
20 years ago, ~all Facebook users were organic real life social networks chatting with each other online.
It's not gone yet, but for many years, that "organic social network" usage segment has been declining.
The commercially motivated "social media influencer marketing" segment has been growing faster than the "organic" segment has been declining.
It's just a huge change from the early days of social media (Instagram 1.0, Flickr, Twitter, o.g. Facebook), where nearly everybody who was active on the platform was also posting.
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.