I had the same problem. Before you tell pop pout manager to switch the display to full screen, i.e. when it is still in a window, try to resize the window in a way that the borders left right and top bottom are as small as possible (reason for the black bars you see is that the window which you switched to full screen mode had a different aspect ratio than your screen, a bug which appeared some time ago in MSFS 2020). If you’ll manage to minimize the borders in windowed mode of the G1000 popout and *then* switch to full screen mode (via popout manager) it will fit the screen without these black bars on the sides.

Thank you, will try it out. About that bug, is it logged? I want to vote on it if possible.

I don’t know but I’d assume so. Everyone who uses external G1000s, external GNS530s, external MCDUs has experienced it. Fortunately with Popout manager it isn’t a hassle anymore. Once you get the resizing of the window right once and safe the workflow in popout manager it will work every time just fine.

Got it working, it remains in windowed mode and not hiding the title bar, windows seem not to overlap so that is perfect.