I think we should take it as a given that countries try to influence the citizens of other countries using social media. We know for a fact that there are state-run influence campaigns on Facebook, Instagram, Twitter, etc. That evidence has been well-researched for many years now. And I'm not just talking about China, Russia, etc.; I expect US intelligence agencies also use social media to influence our adversaries.

It's absolutely absurd to think that the Chinese government doesn't use TikTok to influence non-Chinese users. They'd be incredibly foolish not to do so. And the difference here (as compared to other nations, including the US) is that that Chinese government gets to legally, deeply meddle in the affairs of Chinese companies as a matter of course. Running influence campaigns on a platform owned by a company out of the Chinese government's reach is a bit more work; they get to do it essentially "for free" on TikTok, plus, as a bonus, they'd have access to data they wouldn't get from a foreign-owned platform.

I think any country should have the right to protect its citizens from influence campaigns led by other countries. Whether or not that protection can and will be effective, and whether or not it's a smokescreen for other purposes (e.g. protecting Meta's market share), is another matter, of course. And certainly some kinds of protection -- such as a US TikTok ban -- will be wildly unpopular with a lot of people who love using it.