Kirigami apps not loading dark theme

Ever since the Neon updated to Plasma 6.0 I have a problem with Kirigami apps not loading dark theme correctly. Here’s a Quick Settings KCM displaying light background with light font color when set to dark mode:

When starting, systemsettings complain about about a missing theme “Fusion”:

kf.kirigami.platform: Failed to find a Kirigami platform plugin for style "Fusion"

I’ve created a new account but the problem persists, could there be a problem with the installation itself or some old /etc config files? I’ve also tried to compare the installed breeze packages to a live CD Neon, but there are no obvious differences. I’ve seen some similar reports, but without a solution.

There’s a workaround to start these apps with QT_QUICK_CONTROLS_STYLE=org.kde.desktop systemsettings, the theme then loads properly.

Any clues what could be the cause of it?

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Running into the same problem some time ago. Not certain if related but it seems like all of this started happening for me since qt6. Dolphin file manager also is struggling with some icons being black and others white. Opening Kdenlive from a .kdenlive fine will also have white backgrounds and white texts and some parts will be dark theme.

So far I found nothing to actually fix this and looking up what message I got took me here.

Please check if you have the package plasma-integration installed

Is installed. Any other ideas? Been trying to fix this for the past 2 days, cleared cache without any result as well. Switching QT_QPA_PLATFORMTHEME between qt5ct and qt6ct also has no results.

It was indeed an ancient version of plasma-integration for me, apparently apt didn’t upgrade it to 6.0.2. It also fixed mixed icon colors in Dolphin and Kontact. Thanks!


If you are running KDE Plasma then you should not have qt5ct or qt6ct installed; these packages conflict with plasma-integration. If you are not running KDE Plasma then unfortunately I do not know how to help.

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This :point_up: please make sure you’re not overriding the platformtheme in any way or the QT_QUICK_CONTROLS_STYLE. On KDE Plasma, plasma-integration is supposed to be handling all of that

I had the same issue after the Plasma 6 update (KDEneon user edition).
It was also caused by the plasma-integration package being stuck on version 5.19.5-0xneon+20.04+focal+build11.

But neither doing a pkcon update nor apt update && apt full-upgrade found any available updates.

The cause for this were apt preferences defined under /etc/apt/preferences.d, specifically 99-plasma-integration which pinned the package to version 5.1*. This seems to be a remnant of an old version of neon, as I am using neon on this device since 2018 and have been upgrading neon from then without doing a fresh reinstallation.

So if anyone has the same issue as I had, check your /etc/apt/preferences.d directory for remnants.
For reference, a fresh, up-to-date neon install currently only contains the following files: 50-neon-ubuntu-release-upgrader 99-jammy-overrides 99-neon-base-files org-kde-neon-net-launchpad-ppa-mozillateam-pin.
Meanwhile, my current installation additionally contained: 99-neon-software-properties 99-plasma-integration 99-pulseaudio-qt.