I'd imagine it works like movie ratings. You don't filter movies from scene to scene. There's just one rating for an entire site or app.

But yeah I get the point, API based solutions are complicated and brittle because they require all services to implement it properly. In contrast a user-set app installation password in the OS settings is more effective and easier to implement.

If a chronological social media feed contains both R and G rated elements how would you implement that?