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There are so-so approximations of it, like the guardian vpn/firewall: https://guardianapp.com/

Unfortunately the approximations are not that great, requiring you to route all your network traffic through an unknown company.

There's also https://lockdownhq.com/ which should work on device. There really should be something like Screen Time directly integrated in the OS.

I'm sure there are open-source versions you can self-host