There's been some vulnerabilities exposed but I think overall "sketchy" can be subjective. https://www.wired.com/story/tiktok-ban-us-national-security-...

A recent example is the app was caught reading the user clipboard in iOS 14 beta but a lot of other apps were also caught red handed. The oft-cited national security risk about ByteDance providing user info to Chinese government is a bit overblown, when the NSA has been spying on its own citizens for years...