> How is it not a form of digital heroin

Because "digital heroin" is a nonsense phrase used as a thought-terminating cliché.

> when the side-effects are the same of?

Assuming that this is intended to be something like "when the side effects are the same as those of heroin?" then the premise is false; the effects (side or otherwise) of TikTok are not meaningfully similar to those of heroin.