The display option sidebar is just on-wiki javascript. So, it can't be done directly in the ProofreadPage extension.

I understand under normal Desktop mode, the side-bar portlet Display options hosts some formatting options -- including the one that toggles embedded pagenum[ber] display on or off, regardless of them being set to ''inline'' or to ''left margin'' display -- is local JavaScript based, but I'm not sure if the creation of links upon transclusion themselves ( the pagenum template's role ) is also completely part of local JavaScript as well. If you say link-generation using that template has no role in/with the PrP extension itself, then that settles that point.

For Mobile view, embedded Page: links in a virtual left margin is unrealistic if not just problematic. There is no side-bar in Mobile view so the portlet is also not feasible; neither are any of the resulting Dynamic layout displays. All mobile view needs is the ability to generate inline page links as depicted in the attached image in this Task's description pane and a single top button to toggle the display of these inline pagenums on or off (of course off would be the click-in default).

Is that more clear to what the requested enhancement should be?