When embedded PDF Resources are included in a course lesson, they open as pop-ups when clicked in the new membership site layout.
It could still be valuable to have a PDF shown as expanded, with the PDF content visible right inside the lesson without covering the rest of the lesson content. PDF Resources have been working like that for a long time in the old membership site lesson layout, so some courses may be set up to depend on readers actually being able to SEE the PDF content right away when viewing the lessons.
Could this possibly be solved by relocating the Resources block to the main content column of the course layout? Maybe as a configurable option?