Public bug reported:

Package: sddm

Version: Ubuntu 25.10 (Questing) 0.21.0+git20250502.4fe234b-2ubuntu1

Description:
When a user configures their display layout in KDE System Settings → Display 
and Monitor and clicks Apply, the configuration is saved to 
~/.config/kwinoutputconfig.json. However SDDM, which runs as its own system 
user, has no access to this file and retains its own independent display 
configuration.
On a dual monitor system this results in the SDDM login screen displaying 
monitors in a different arrangement than the KDE desktop session. Specifically, 
mouse cursor movement between monitors on the login screen does not match the 
configured layout in the desktop session, making the login screen confusing to 
use.

Steps to reproduce:

Install Kubuntu 25.10 on a system with two monitors
Configure monitor arrangement in KDE System Settings → Display and Monitor, 
including relative positioning
Apply the configuration
Log out or reboot
Observe that the SDDM login screen uses a different monitor arrangement than 
configured

Expected behaviour:
SDDM should use the same monitor arrangement as configured in KDE display 
settings, either by automatically syncing on apply, or by providing a UI option 
to apply settings to the login screen.

Actual behaviour:
SDDM retains its own independent display configuration. The workaround requires 
manually copying ~/.config/kwinoutputconfig.json to 
/var/lib/sddm/.config/kwinoutputconfig.json with correct ownership set to the 
sddm user.

Workaround:
in bash: sudo mkdir -p /var/lib/sddm/.config
sudo cp ~/.config/kwinoutputconfig.json 
/var/lib/sddm/.config/kwinoutputconfig.json
sudo chown -R sddm:sddm /var/lib/sddm/.config
Additional information:

Laptop screen: eDP-1 (1920x1080)
External monitor: HDMI-A-1 (1920x1080)
Session type: Wayland

** Affects: sddm (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: display kde multiple-monitors sddm

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https://bugs.launchpad.net/bugs/2142661

Title:
  SDDM display layout not updated when KDE display configuration is
  changed

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