SUMMARY The headline says everything. The menu only appears when I drag the window onto the primary monitor. SOFTWARE/OS VERSIONS KDE Plasma Version: 5.20.5 KDE Frameworks Version: 5.78.0 Qt Version: 5.15.2
Well, I should maybe add what I would expect. I think the global menu should appear for the currently active window.
I confirm the issue. Using Global Menu on Primary screen, dragging for example a Dolphin window to second monitor: booh, there is no Global Menu anymore for Dolphin when that window is in focus. Operating System: Mageia Cauldron KDE Plasma Version: 5.21.5 KDE Frameworks Version: 5.82.0 Qt Version: 5.15.2 Kernel Version: 5.12.4-desktop-1.mga9 OS Type: 64-bit Processors: 4 × Intel® Core™ i5-6600K CPU @ 3.50GHz Memory: 15.6 Gio of RAM
I can also confirm this issue, at least on Wayland. Operating System: KDE Neon KDE Plasma Version: 5.22.2 KDE Frameworks Version: 5.83.0 Qt Version: 5.15.3
I'm suffering the same problem in my laptop. Operating System: Debian GNU/Linux KDE Plasma Version: 5.24.4 KDE Frameworks Version: 5.90.0 Qt Version: 5.15.2 Kernel Version: 5.16.0-6-amd64 (64-bit) Graphics Platform: X11 Processors: 4 × Intel® Core™ i5-4200U CPU @ 1.60GHz Memory: 15,6 GiB of RAM Graphics Processor: Mesa DRI Intel® HD Graphics 4400
You need one on each screen, just like how it is on MacOS.