I wonder if the lounge will allow J pax transiting from London/Rome but onto another domestic flight?

The generalisation you mention isn't true at all, generally all F seats are released and available to anyone with a ticket (full fare, sale or award) and it is a free for all. If you are an upgrade, then, well of course you are limited to what remains.

The image on this article is misleading - the Touch Bar Macbook Pros are not affected, it is the earlier generation Retina models affected by this.

That first cocktail looks hideous. United always seem to have a problem with the fine details.