SUMMARY
Unable to switch from the laptop screen to an external monitor connected via DisplayPort, despite the external monitor being correctly displayed in the System Settings' Display Configuration.

Switching from the external monitor back to the laptop screen works without issues.

A workaround involves running the following xrandr command:
$ xrandr --output DP-2 --mode 2560x1440 --rate 164.83 --primary --output eDP-1-1 --off
Occasionally, this command must be run twice — once to wake the external monitor from sleep and again to fully activate it.

STEPS TO REPRODUCE
1. Connect an external monitor to a laptop via DisplayPort.
2. Activate only the laptop screen and deactivate the external monitor.
3. Select the "Switch to external screen" option in the System Tray's Display Configuration. 

OBSERVED RESULT
The laptop screen turns off.
The external monitor remains in sleep mode and does not turn on.
It seems that Kscreen considers the switch successful, but the external monitor stays inactive. To recover, the external monitor must be turned off and on again, which restores the desktop to the laptop screen.

EXPECTED RESULT
The external monitor should wake from sleep and display the desktop as expected.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Manjaro KDE Stable
KDE Plasma Version: 6.2.4
KDE Frameworks Version: 6.8.0
Qt Version: 6.8.1

ADDITIONAL INFORMATION
Graphics Platform: X11
Graphics Adapter: Nvidia TU106M + Intel UHD Graphics 630, Nvidia set as primary GPU
Graphics Driver Version: 550.135