In KDE Plasma Ctrl+F4 not working because it combination is used to switch KWin display. You need to change default combination for display 4:
![](https://andjey.info/wp-content/uploads/2020/05/kde-plasma-kwin-1024x607.jpg)
In KDE Plasma Ctrl+F4 not working because it combination is used to switch KWin display. You need to change default combination for display 4: