Cursor focus not detected by the mouse wheel.

[robkam]

Operating System: Kubuntu 20.04
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.8.0-59-generic
OS Type: 64-bit
Installed .deb from https://github.com/sezanzeb/key-mapper and set mouse buttons with:
Wheel Down > KEY_PAGEDOWN
Wheel Up > KEY_PAGEUP
Button SIDE > Control_L + BTN_LEFT
Button EXTRA > Shift_L + BTN_LEFT

For example in Mozilla Thunderbird classic view without Key Mapper whichever pane (folders or messages) the cursor hovers over the mouse wheel scrolls that one. With Key Mapper I have to first click on whichever pane I want to scroll.