Who's fault is the resulting good or bad is a separate question than is the result good or bad, but I'll dip a toe.

I don't think code can yet have responsibility, but the company that creates it can, as well as the companies that help distribute it. If it were discovered that an app was causing people to explode, I'm sure you'd then find the logic required to shift some blame away from the people being splattered. As for how exactly responsibility should be divided in light of varying levels of potential harm, I don't have a well formed opinion.

Personally, as a "fucking adult", I choose not to use TikTok as I find short form video streams to be like mind cancer.

Edit: ...like mental heroin. Thought of a better analogy.

Edit2: I can't help but think of that as I read through comment sections discussing TikTok these days. Likely a good percentage of people commenting are junkies being threatened with their source getting cut off and it shows. "TikTok is bad? Well then its all bad, man, might as well delete the internet!" lol.