We're actually not sure how you would have ever gotten it working the way that you describe on Windows. The slideshow was never really designed to be run in the background, and as soon as I click anywhere on the display not running the slideshow on Windows, the slideshow ends immediately. The same actually happens on the MacOS for me as well, so while I agree that there is some weirdness with what you are describing is happening (it sounds like you can still see the slideshow happening but its behind the other windows on that display?), if we get your slideshow is working as we expect it to, it is still not going to do what it sounds like you are hoping it will. Would putting the Preview window in full screen mode with all side panels hidden essentially achieve what you were doing on Windows?