Add `minimize all windows` addon to your panel or your desktop, set a keyboard shorcut (I use meta+d). Nothing happens when I press the shortcut, it works under X11 session.
Confirming this bug in: Distribution: KDE neon Developer Edition Unstable Branches live iso 20170813 KDE Plasma Version: 5.10.90 KDE Frameworks Version: 5.37.0 Qt Version: 5.9.1 Kernel Version: 4.10.0-32-generic OS Type: 64-bit Video Card: Intel 4500MHD Both clicking on created 'Minimize Windows' desktop/panel widgets and activating assigned to it key combination (Meta+D) aren't minimizing windows. Default shortcut for 'Show Desktop' - 'Ctrl+F12' is working, assigning 'Meta+D' combination to it in 'Global Shortcuts' and activating 'Show Desktop' action with new 'Meta+D' combination is also working.
I just had a look into the implementation. This cannot work on Wayland. It needs a completely different implementation on Wayland.
*** Bug 374977 has been marked as a duplicate of this bug. ***
I think the easiest would be to use libtaskmanager which can minimize windows and would remove the need for a C++ plug-in as it provides a QML import.