Parental controls are complicated and obscure, IME. Setting up a child to play Minecraft through Microsoft was like setting up a web server with firewalls and reverse proxy... only less sensible. I'd appreciate that is so they can get parents to set accounts as 'adult' so Microsoft can exploit them.

You can set up, for example a child friendly DNS (Family version of OpenDNS) then Firefox come along and bypass it (DoH).

Probably, we need an OS level setting, per account, browsers would need to expose it to websites, apps installed would have to check and provide content according to local legislation/rules. Bypasses would have to be performed by an "adult" account.

The main issue is that adults would be able to set themselves as children and avoid negative commercial activity. That's a problem because it means FANG, etc, will lobby against it and then ensure their implementations are convoluted and broken.