SUMMARY

I have a dual monitor setup (2x 1920x1080) where I am extending my Desktop to the other monitor in order to have more screen space to work with. I am using the "extend to the left" option while the left screen is marked as my primary screen.

If I open Okular on my right screen and open one of the dropdown menus mentioned below, the menu doesn't open where my cursor is. In fact it doesn't even open on the correct (right) screen. Instead it opens at the right edge of my left screen (even though Okular is completely rendered on the right one and there'd be plenty of space to render the menu on it).
The y-coordinate of the opened menu seems to be chose properly. It is only the x-coordinate that seems to be affected.

STEPS TO REPRODUCE
1. Open Okular on the right screen
2. Open one of the dropdown menus mentioned below

AFFECTED MENUS
- Dropdown for switching the selection mode (text, area, table)
- Dropdown for quick annotations (menu only shows "Configure annotations")
- Dropdown for choosing the arrow annotation type
- Dropdown for choosing the "marker" annotation type ("Approved", "Not approved", etc)

UNAFFECTED MENUS:
- All dropdown menus for the entries in the actual menu bar (File, View, Edit, ...)
- Dropdown for selecting zoom level


SOFTWARE/OS VERSIONS
Operating System: KDE neon 5.20
KDE Plasma Version: 5.20.1
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.0
Kernel Version: 5.4.0-52-generic
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-4770 CPU @ 3.40GHz
Memory: 7,7 GiB of RAM
Graphics Processor: NVE4