I don't personally use TikTok, but I'm not sure that I'd care much if they know that I like to watch videos about pottery or gaming or whatever. Google / YouTube certainly knows already.
2. They push you to engage with that content, leaving comments and sending messages.
3. They have the capability to make you watch content that they know you'll like with the express goal of getting you to react to it.
4. TikTok videos are often recorded in personal spaces, giving insight into individuals' lives and leaking personal information (partners, children, pets, etc.).
5. The app itself can collect information about you and your device, including any information it may have access to you through overly-broad permission collection.
2+3. Why should I worry that a company is serving me stuff I actually like in hopes I'll interact with it? Isn't that the social contract of digital advertising, except TT is actually delivering value to the consumer?
4+5. That's just table stakes for the industry.
"Table stakes" and "a tool for surveillance" are not at all mutually exclusive. Which is all the more reason to be concerned about Mudge's suggestions that foreign bad actors were employed at Twitter. Make no mistake: social media is a tool that can be used for malicious purposes.