Unable to launch Qt-based application using pkexec

[Norbert]

Steps to reproduce:
1. Have Ubuntu 20.04 LTS installed
2. Login to Plasma session
3. Try to execute Kubuntu Device Drivers application using

    pkexec kubuntu-driver-manager

Expected results:
* application launched normally with root rights

Actual results:
* application crashed with the following output in the terminal -

```
qt.qpa.xcb: could not connect to display
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: wayland-org.kde.kwin.qpa, dxcb, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.

Aborted (core dumped)
```

Affected applications: Kate, Krusader, Krita, Konsole
Not affected apps: Pluma, Caja

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: policykit-1 0.105-26ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-39.43-lowlatency 5.4.41
Uname: Linux 5.4.0-39-lowlatency x86_64
ApportVersion: 2.20.11-0ubuntu27.3
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Mon Jun 29 20:56:49 2020
InstallationDate: Installed on 2020-04-22 (67 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Release amd64 (20200422)
SourcePackage: policykit-1
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Norbert (nrbrtx)]

The applications in this bug do not have related files in /usr/share/polkit-1/actions . So this behavior is expected.