What for? I use family link for my kids devices. It works good enough. Everything else seems way too intrusive.

Apple is horrible in this regard. Their solutions never really work.

A joint venture for an (optional) cross-platform family app would be more than enough. This, plus a (voluntary) content rating that's offered via an API (could even be simple meta data on a webpage). Done.

Nice. How does pornhub.com "verify" your age when accessing it from your family computer's Ububtu account "my kids account"?

Oh, there is no config to retrieve, no We API to speak to.

"I'm 18 or older"-button it is. Is that a workable solution?