SUMMARY
I have a laptop connected with an external monitor. After updating to Plasma 5.20, when I open the activity switcher on the external monitor, it opens on the laptop monitor, while when I try to open it on the laptop monitor it just doesn't show (at least when the external monitor is connected).

STEPS TO REPRODUCE
1. Connect at least two displays to the system (laptop + external monitor, in my case)
2a. Open the activity switcher on the non-primary monitor (e.g., right click on the desktop of the non-primary screen, "Show Activity Switcher")
2b. Open the activity switcher on the primary monitor (e.g., right click on the desktop of the primary screen, "Show Activity Switcher")

OBSERVED RESULT
2a: The activity switcher opens on the primary monitor
2b: The activity switcher does not open

EXPECTED RESULT
2a: The activity switcher opens on the non-primary monitor
2b: The activity switcher opens on the primary monitor


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux
KDE Plasma Version: 5.20.0
KDE Frameworks Version: 5.75.0
Qt Version: 5.15.1

ADDITIONAL INFORMATION
- This can be reproduced also by using other methods for opening the activity switcher (e.g., the "Activities" switcher or the keyboard shortcut);
- The resolution of my primary monitor is 1920x1080, while the one of my external monitor is 2560x1440.
- The version I selected for the bug report is "master", while it is 5.20, actually: 5.20 was one of the options I could select at the time I submitted the bug report.