It's TikTok. Funny jokes and dance videos. And they're collecting no more than American IT companies are doing.
"I just can't believe that a powerful country like America is letting a not-so-friendly military/civilian complex infiltrate it for somewhat unknown purpose."
Are you for real? The one country that fits the description of not-so-friendly military-complex is the U.S. itself.
A more pressing problem and question is that despite everything we learned from the CIA and NSA leaks, American companies and their software is inside every country, government, business and IT infrastructure, and is collecting vast amounts of sensitive data still to this day.
All while people like you are drawing attention to TikTok.