There's an arguable national security angle. Potential surveillance, and, especially, manipulation and dumbing-down.
Earlier, I also heard complaints about TikTok implications for individual health. Which, when implying US Big Tech social media as an acceptable alternative, sounds like an abusive parent: "If anyone's going to beat up my kids, it'll be me!"
Sounds like US Big Tech might've decided on the complaint angle of "some other country could spy on people" -- since all the other valid complaints about TikTok, including intimate surveillance, also apply to TikTok's counterpart US Big Tech products.
Outlaw the irresponsible behaviors, not the competition.