Ofcom has a clear guide on how harmful to minors is defined. It is even clearly referenced in your own links:

https://www.ofcom.org.uk/siteassets/resources/documents/cons...

Your own links also reference the fact that moderation of content by platforms will allow them to comply with the law.

I don’t like this law and not here to defend its existence. But it is factually untrue just adding this would mean you also need to age verify users.

Case in point (which is not a rare use case), I use webrtc signalling to establish data connections in a multiplayer online game. Why would that require age verification when users are unable to send random content to one another?