SUMMARY
Toolbar pop-up menu always shows in left-most display

STEPS TO REPRODUCE
1. Add an action that comes with a pop-up menu to toolbar, e.g. 'Sort By', 'View Mode', etc.
2. Move Dolphin out of the left-most display
3. Click on the action button

OBSERVED RESULT
Menu shows up next to the right edge in the leftmost display.

EXPECTED RESULT
Menu shows right under the button.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.15.0
Kernel Version: 5.6.15-zen2-1-zen
OS Type: 64-bit

ADDITIONAL INFORMATION
XRandR output:
Screen 0: minimum 8 x 8, current 11520 x 2160, maximum 16384 x 16384
HDMI-0 connected 3840x2160+7680+0 (normal left inverted right x axis y axis) 476mm x 268mm
   1920x1080     60.00*+  59.94    50.00    60.00    50.04  
   1680x1050     59.95  
   1440x900      59.89  
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1280x720      60.00    59.94    50.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94    59.93  
DP-0 connected 3840x2160+0+0 (normal left inverted right x axis y axis) 381mm x 214mm
   1920x1080     60.01*+  40.00  
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 connected primary 3840x2160+3840+0 (normal left inverted right x axis y axis) 597mm x 336mm
   3840x2160     60.00*+  29.98  
   2560x1440     59.95  
   1920x2160     59.99  
   1920x1080     60.00    59.94    50.00  
   1680x1050     59.95  
   1440x900      59.89  
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1280x720      60.00    59.94    50.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94    59.93  
DP-4 disconnected (normal left inverted right x axis y axis)

KDE Global Scale: 2.0