The KDE keyboard shortcut for the Minimize (minimize active window) action is not set by default in KDE. However, it is available in the KDE System Settings under Shortcuts > Global Shortcuts > KWin. There, you can create a custom keyboard shortcut for Minimize Window. The recommended keystrokes are Alt F9 for PC or option F9 for Mac, to be consistent with other desktop environments. This keyboard shortcut may also be available with other desktop environments that can be run on Linux and set by default.