I have a new 15" MacBook Pro which of course has a built-in display.
I also have the optional monitor sold by Apple. It is the LG Ultrafine 27" (5K) monitor (a super great display.)
From the Lightroom Slideshow panel, when I press the Play button, it always runs the slideshow on the MacBook built-in screen... but I want it to run on the secondary monitor (the 27" LG.) I have found no option to designate the slideshow target monitor. Please help because I need to show the slide shows on the larger screen.