Hi Armin,
I really like how the website https://mgabrilo.work/project/demon-charlie-constantinou shows a small preview of the next "slide." It could be a great feature for the fullscreen slider as well. While I know it can be done manually, having it as an option would offer some advantages. For example, it could allow you to position the preview image with a single setting, like in the bottom right corner or next to the mouse cursor.
Or even having small preview images in a row as you can see here: https://www.dailydialogue.cc