[Bug 2130871] Re: software-properties-qt fails to start with pkexec on Wayland: “Could not load the Qt platform plugin 'xcb'”

[Clay Weber]

*** This bug is a duplicate of bug 2129765 ***
    https://bugs.launchpad.net/bugs/2129765

** This bug has been marked a duplicate of bug 2129765
   Kubuntu 25.10: Clicking on "Software Sources" within Discovery, doesn't launch ubuntu's software-properties

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https://bugs.launchpad.net/bugs/2130871

Title:
  software-properties-qt fails to start with pkexec on Wayland: “Could
  not load the Qt platform plugin 'xcb'”

Status in software-properties package in Ubuntu:
  Confirmed

Bug description:
  When running pkexec software-properties-qt on Kubuntu 25.10 (Plasma
  6.1, Wayland session), the application crashes immediately with a Qt
  platform plugin error related to “xcb”.

  This issue only occurs under Wayland; the same command works correctly
  under X11 or when run with sudo.

  Steps to Reproduce

  1. Log into Kubuntu 25.10 using Plasma (Wayland).

  2. Open a terminal and run:
  pkexec software-properties-qt

  3. Observe the crash.

  Expected Result

  The Software & Updates dialog should open normally with administrative
  privileges.

  Actual Result

  The application aborts with the following error message:

  qt.qpa.xcb: could not connect to display 
  qt.qpa.plugin: From 6.5.0, xcb-cursor0 or libxcb-cursor0 is needed to load the Qt xcb platform plugin.
  qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
  This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

  Available platform plugins are: minimalegl, wayland, vkkhrdisplay,
  eglfs, offscreen, wayland-egl, vnc, minimal, linuxfb, xcb.

  Aborted (core dumped)

  Additional Information

  * Package version: software-properties-qt from Kubuntu 25.10
  repositories

  * libxcb-cursor0 is installed and up to date.

  * Running sudo software-properties-qt works fine.

  * The GTK version (software-properties-gtk) runs without issues.

  * This appears to be a Polkit or Qt platform integration bug under
  Wayland.

  Workaround

  Logging into Plasma (X11) allows the application to run normally.

  ProblemType: Bug
  DistroRelease: Ubuntu 25.10
  Package: software-properties-qt 0.114
  ProcVersionSignature: Ubuntu 6.17.0-6.6-generic 6.17.1
  Uname: Linux 6.17.0-6-generic x86_64
  ApportVersion: 2.33.1-0ubuntu3
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: KDE
  Date: Fri Nov  7 12:30:16 2025
  InstallationDate: Installed on 2025-01-12 (299 days ago)
  InstallationMedia: Kubuntu 24.04.1 LTS "Noble Numbat" - Release amd64 (20240827)
  PackageArchitecture: all
  SourcePackage: software-properties
  UpgradeStatus: Upgraded to questing on 2025-11-07 (0 days ago)

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