There's an annoying issue on SteamWorks extension that I hope can get fixed on the next update...
It pairs the overlay to the EditWindow, this means extensions that manipulate the EditWindow (like Ultimate Fullscreen object) will result in a stretched, cropped off-screen overlay.
I was hoping the overlay could be changed to pair with the MainWindow if possible (as long it can display above the EditWindow) or maybe it would be necessary to create a new Window above the EditWindow were the overlay would show, the same size and position as the MainWindow.
It's one of the reasons people have stopped using Ultimate Fullscreen, which is really important to get pixel perfect resolutions in fullscreen.
I'm making a unofficial update for Ultimate Fullscreen, I was looking for a way to fix the Steam Overlay myself but I can't figure out how to do it, maybe it can only be done from the SteamWorks extension.