The “Page Management” takes up much more space that necessary. There is no need of all the space for Page title, master and notes.
In 2.x it took up the space it needed and it was possible to leave it open and work in the plot at the same time. That it not possible any more – at least not on my screen with screen resolution 1920 x 1080.
Could you please reconsider the layout?
Maybe you could make it act as the “Plot configure” dialog.
The “Defined Behaviours” panel is OK.