Due to China's "security" laws security and intelligence agencies have essentially full access to large companies' data. There's no real due process so a "private" company's data is essentially government data. There's also the overt and covert censorship and propaganda imposed by the government.
Company executives serve at the pleasure of the government. Anyone not towing the party line or acting with too much independence will get caught up in "anti-corruption" investigations or just be arrested for crimes they may or may not have actually committed.
Realistically it's better to just assume a priori that a Chinese social media company is pushing propaganda and building dossiers of users. It's certainly safer to assume that.
That's just "official" propaganda. The CCP's various astroturfing brigades are well documented (see "50 cent army" and "internet navy"). They show up in public forums of all stripes.
TikTok doesn't allow discussion of the Tiananmen Square massacre, Falun Gong, Free Tibet, or anything other topics the CCP deems inappropriate. That censorship is propaganda by omission. Content users see being primary algorithmic makes it trivial to add in pro-CCP or just anti-West content into people's feeds.
A lot of people in comments are talking about how great the feed algorithm is out weeding out teenage dance videos and showing interesting content.
You can easily imagine a scenario where CCP tweaks its algorithms to favor content relating to one party or candidate vs. the other.
The scary part is that I think it wouldn't be obvious to know whether China is exploiting TikTok's American audience via algorithms driving a certain agenda since it can be done very subtly in non-obvious ways.