Sure you can create a sandbox that can cater for some app and keep it completely isolated. And yes, whereas previously any app could basically see and do anything, now there are limits at the OS level.
But an app that shows the latest cat video needs connectivity and the server serving that car video now tracks when you were watching it.
And no one, not even Apple, complains about that kind of tracking nor attempt to stop it.
This is a ridiculous example
Yes, but there’s no way to stop that kind of tracking since those app require you to sign in.
The current App Store already has this kind of tracking.