rooting – Need to configure a phone with limited permissions to help solve learning problems

I need to set up a phone that will allow the user to access the installed apps but will not allow them to install new apps. In addition, I must only allow access to a whitelist of websites. These constraints must be unbreakable at the origin of wiping in the factory. Regarding privacy, my idea was to have a superuser account, with the user and the administrator each having half the password. The administrator can not connect to the phone without the user's permission.

I am a bit desperate here. I've asked this question twice on the Android root and both times, people have said to install applications that "reward good behavior" and so on. We are well beyond this point. The user really needs emails, texts, maps and some work-related applications (most certainly some apps like Habitica to reward good habits!).

I have not used a phone yet, but I am quite competent technically. If Tasker is part of the solution, it suits me pretty well, otherwise I will do or learn all that is necessary for this to happen. I have a Google pixel to work with, but if absolutely necessary will get a different phone.

Thank you very much for any help you can provide!
p.s. the disorder is a pretty powerful executive function disorder – despite 18 years of therapy with 6 different people, the user is basically unable to create good habits or to show a lot of willpower. It was rather devastating for them.