I dunno what's worse, the way it rots their brains by sucking in all their attention or how they use it to bully one another.
It's all shite for kids. Algorithms automatically push harmful content (eating disorder/self-harm stuff, rage bait, nuisance streamers, whatever else) and kids' brains are literally not developed enough to tell what is good content, and what is bad or harmful content. Hell, adults can barely do that. I watched a YouTube video recently about how CocoMelon is designed to be addictive to children - Everything from the colors they use to the amount of time between cutting from one scene to another. It's all to make a buck.
The bullying is another shitty aspect because if a kid's getting bullied at school now it can happen at home too from the same people. I'd imagine most kids don't want to block people because they think it's a sign of weakness as if they "can't handle" the bullying. Or they think it will bring some other form of social ostracizing..blocking them online doesn't block them in real life. The threat/thought of increased severity of bullying in real life from blocking someone online has to be another big source of anxiety for someone already being bullied.
f***ing kids, man.