https://www.afterbabel.com/p/industrial-scale-snapchat
The archive also includes a bunch of articles on social media in general, edtech, and similar.
Yeah, it's not "moronic propaganda", it's someone who has, historically and famously so, been very focused on the broad issue of social media's impacts focusing in on various specific aspects of it, of which TikTok is a part.
OP seems, respectfully so, ignorant to who Haidt is and would perhaps do well to read up on more of his output (apologies to OP if this assumption is incorrect).
The damned site he writes under is called After Babel! His identity at its core is linked to not just convincing but aggravating agitating and hyping an image of the world made "anxious" and depressed by devices.
There's a lot of other causes for the world being as unsupportive as it is. As a society we are losing meaningful connection to work, by having such vast mega corps sucking up all the work, managing the world from the top down. The concentration of capital has had enormously brutal impacts on the human spirit. But you won't see Haidt acknowledge or concern himself with what else is unravelling the human fabric.
There's some directionally correct concerns Haidt has, but as someone whose made it his calling to drive a wedge into what society is & demand a conservatism against the new, stridently & loudly, with no bones about what comes very close to lying, I cannot help but detest him deeply.
The evidence for this is far weaker than social media causing harm, but let's assume that you're right. All these problems caused by capitalism seemed to manifest during the the rise of social media tech giants, so they would still be the most likely culprit. I'm usually the person who defends capitalism, but even I review content recommendation systems on social media as capitalist brainwashing machines. I don't think being too conservative with limiting access to children is a bad thing.
He's a noted grifter with many years of making stuff up.