Haidt is first on my personal list of "people who don't really know what they're talking about but who I nonetheless mostly agree with." The "If Books Could Kill" show did a good episode about some of his works that indicate he has a fairly nonrigorous methodology and implements some iffy statistical controls to support what is probably a pre-conceived viewpoint. He doesn't have the best reputation in the academic space he operates within.

That being said, this stuff is hard to study, and I have no doubt that things like social media and AI are bad for a developing brain even if you can't arrive at a statistically satisfying conclusion. I can tell that this shit is bad for me, and I'm a fully grown man.