Steps to repdroduce: - On linux, open a KDE/Wayland session - connect an external monitor => the wallpaper displays on the external screen, so it works - now open an impress presentation - start the presentation mode => the presentation does not display on the external screen I reported this bug against Kwin, but they said it is not their bug: https://bugs.kde.org/show_bug.cgi?id=451852
So I tested again the KDE/Wayland session with KDE 5.25.4, and now impress presentations for correctly on the secondary screen. Closing as WORKSFORME.
Forgot to add that this is on Debian testing, with LO 7.4.1.