Children screen time restrictions broken

We gave our son an iPhone and are using screen time restrictions to ensure that he uses it mostly for communication with family and class mates and not for endlessly watching youtube. Unfortunately, he manages to evade the screen time restrictions again and again and I'm not sure how he does it. I've already changed the screen time password twice, so I doubt he knows that.

There are ways in which screen time restrictions are provably broken. For example, when deleting an app, all the recorded screen time for that app disappears. Effectively, this means that my son can watch youtube without being detected by installing it, binge watching all night, and then deleting the app again. By deleting the app after watching, all the recorded screen time disappears retroactively. So one cannot rely on Apple's screen time tracking.

This would not be a big problem if I knew how to block the installation of once approved apps. When my son tries to install a new app, I get an app installation request that I can approve or deny. But once an app is approved, it seems it can be deleted and reinstalled without further approval. Can this somehow be changed so that every reinstall needs an approval?

Also, it seems to me that there are ways to evade the screen lock. My son says he doesn't know how it is possible that he can watch 1 hour of youtube even though the screen limit is set to 15 minutes per day. He says sometimes it works and sometimes it does not. My suspicion is that the screen time is somehow not applied after an app has updated itself? Could that be a possibility?

In any case, help on how to better track and control the screen time on my sons device would be greatly appreciated.