To me, it's more regulating the behaviour of people than regulating the developers of intentionally addictive and intentionally poorly-moderated systems.

The big hegemonic tech platforms, as they currently exist, are not just harmful to adolescents, they're harmful to society as a whole.

I also don't enjoy the prospect of how a ban like this might be implemented in terms of age and identity verification, since I expect it's going look like "hand the data brokers even more of your personal data, they pinky-swear they'll only use it to comply with the law".