Keyboard - Win-keys start menu

KDE Control Center->Regional & Accessibility->Xkb Options

[X] Enable xkb options
- Third level choosers
* Press any of the Win-keys to choose 3rd level

KDE Control Center->Regional & Accessibility->Keyboard Shortcuts
Shortcut Schemes->Global Shortcuts

- Panel
* Popup Launch Menu

Shortcut for Selected Action

(O) Custom

[Advanced]

(O) Alternate shortcut

- press the Win-key (ISO_Level3_Shift)

***

- alternatively, when using custom .Xmodmap, substitute

keycode 115 = ISO_Level3_Shift
keycode 116 = ISO_Level3_Shift