The way I see it is that TikTok is basically a psyops app. We can argue all day whether it is controlled by the Chinese government, by advertisers, by both, whether it is intentional, what its purpose is, etc. But anything that is free and funded by ads is at the end of the day trying to sway the mind and behavior of its users, that is the name of the game.
So to answer your question, it doesn't /do/ anything that other apps don't. But what it does it does rather effectively, and it isn't controlled by a company that is ultimately beholden to the US government. So from the gov's perspective, TikTok somewhere between a nuisance and a threat to national security.