Assuming you go down the path of allowing online anything, seems like, after doing your best with parental controls, the most effective thing is time boxing screen usage. Only so much can happen in, say, 2-3 30 minute sessions throughout the day, and the chances of a kid deciding to blow their precious minutes responding to some random person seems much lower than if bored and checking messages idly. Being nearby during a healthy sample of sessions to have a pulse on what's going on helps too - usually pretty obvious what they are doing.

But I share the frustration of the author with how unreliable the controls are. Apple screen time controls routinely stop working - especially the one that only allows access to a finite list of websites. I need to check the browser history every week or so to confirm it is still working, and do some dance where I turn off controls, reboot, then turn back on every once in a while. The reason this particular control is important to me is that, even starting with something as pure as neil.fun, ads on that site have proven to be a few clicks away from semi-pornographic sites - it's terrible! And yet, turning off all internet access is such a coarse decision that limits access to things that are generally informational / fun / good (like neil.fun, or sports facts sites).