Hi, I believe you are referring to the famous Amiga screen dragging feature! Unfortunately, that is not possible with Picasso96 RTG UAE screen modes.
It is possible with PAL modes only. For example, launch ChaosPro (in StartMenu > Applications), then right mouse click and select Settings > Screenmode > Fractalscreen > and select PAL: 640 x 512 Interlaced mode. Now you should be able to drag the screen down and see what's behind it - providing you run some other app in fullscreen PAL mode there too, of course.
Moving windows out of the screen is possible with AmigaOS 3.1.4 version
. If you used some other AmigaOS version to install AmiKit, it is also possible to move windows out of screen providing you install PowerWindowsNG patch. But that is not so easy and, unfortunately, it is unstable. Otherwise it would be installed in AmiKit by default.
Hope it helps.