After selecting "Open Multiple Application Windows" in Workspace > Preferences > Operation and then re-opening AECOsim Building Designer, I get a second window (2) which is grayed out, but I cannot move any view windows to it to have 8 view windows open on two monitors.
The preference opens one program session in two application windows. You should see a (1) or a (2) in the header of each application. The one with (1) is the Primary Application.
You can move all dialogs including the Main Menu freely between the two app windows if you click on the small blue cube in the upper left of each view window. You will get a small pop-up menu where you should select "Change Screen". The window will automatically move to the other monitor screen. You can move the various dialogs (modal & modeless (non-modal)) between the applications and move the Toolbars between applications. You don’t have to hold down the Ctrl key unless you want to disable to auto-docking function of the toolbar. The only thing you CANNOT move is the Status Bar that remains in App (1) the Primary App.
You can dock toolbars to all 8 sides of the application windows. Each application has 4 dockable areas/edges (Top, Bottom, Left & Right) x 2 applications. Certain dialogs can only be docked top/bottom (i.e. Level Manager, References) and some just left/right (i.e. Tasks, Models, Element Information). Toolbars are just another form of dialog.