[Boudica]

TikTok is rotting young peoples brains. Being a way to spike dopamine, it is destroying their brains whilst they are still developing. They won’t be able to sit still for even short intervals without twitching like a druggie

I think similar was said of many internet based entertainment platforms in their infancy too (youtube, twitter etc). It will be interesting to see what happens as a result of people spending excessive amounts of time on social media. The brain is incredibly flexible and adaptable so "rotting" may be a strong perspective, but it will change the way people's attention works and how they process information. There are some positive side affects to shortened attention spans too (though generally I don't think of it as a "good thing"). For example: Skim reading to get to useful information and making quicker decisions about what you do or don't need to spend time on. This actually helps me at work because I can jump between tasks very easily.

Perhaps the real issue is as you say, those dopamine hits with instant gratification.