The slideshow view is still in an early stage of development with only a basic set of features.
If you don’t need the auto-advance mode, you could even use the sticky preview feature instead.
spacebar start and stop auto-advance mode which automatically switches to the next images every five seconds by default. ESC leave slideshow mode and return to lighttable view. + or increase delay between each image. up arrow - or decrease delay between each image. down arrow left-click or right arrow or switch to the next image of the collection. right shift-key right-click or left arrow or switch to the previous image of the collection. left shift-key
Hint: To take full advantage of your screen size, put darktable into fullscreen mode by pressing F11 and hide the border-controls by pressing the B key.