KWin does not distinguish PcManFm-qt windows from the desktop which is drawn by PcManFm-qt. Eventually open file manager windows will therefore not be minimized but only blurred. To have “Show Desktop” fully working following steps are necessary:
In lxqt-globalshortcuts ”Show Desktop” keybinding is disabled
No “Show Desktop” plugin on any panel
In KDE Systemsettings > Window Managment > KWin Scripts ”MinimizeAll” is activated
In KDE Systemsettings > Shortcuts searching for “MinimizeAll” a shortcut is set
~/.config/kglobalshortcutsrc
...
MinimizeAll=Alt+D,none,MinimizeAll
...