A constant stream of memes romanticizing and/or normalizing depression, alienation, hopelessness, or any other of those dark states of mind. Often after switching from Home to All, I'd scroll and just keep bumping into these damned things.
It's the volume that I find corrosive and even suspicious, to the point that sometimes I've suspected that the prevalence of these memes may be a deliberate, artificially inflated thing, just one more bot tool in the box for bad-faith actors to nudge as many people as possible to a passive, apathetic, unengaged state of mind.