My concern with tiktok is that it rots your brain like television, but far more effectively because it's rapid fire content constantly tuned to the individual user to keep them hooked on it. It's an instant gratification machine, effectively a drug, that fries people's attention spans. It has people spending hours a day consuming vapid short-form nonsense, and alters their psyche to make them less effective in other endeavors even when they aren't distracted by the app (particularly school, since it hits children particularly hard.)
The medium is the message.