I think what it has done is financially and societally reward people for being aggressively dumb which always happened, but not at scale like this and certainly not in the spotlight of the public eye
Hot take: I don't think social media made people dumber. We've been dumb this whole time.
It's just that you used to have to have a job that people sent their dumb letters to, to notice.
This made "Engaging with fools" an occupational hazard rather than the 24/7 experience it is presently.