I followed a different approach with my son. We gave him a phone pretty early, and didn't even have a lot of rules around it (no family controls, etc).
The agreement I had with him: "Scroll all day, play video games, etc. That is my side of the agreement. And you also do your school work, learn, practice for exams, homework, etc. That is your side of the agreement. I'll trust you. If your grades get worse, i.e. you need help managing device time, we'll review/change this agreement."
We also sat down many times looking at content together, in attempt to teach him what's trust-worthy and what isn't, what's "healthy" and what isn't, etc. And of course we do other things together as well.
So far (knock on wood) my son has managed well - he is 16 now. He organizes his own time, and has learned when to play and when to work. And crucially he has learned when to disconnect from his devices to do what's necessary.
No kid is the same. I am not saying my approach is best or even right, I just offer it as another data point.