Why a KDE global theme installed via 'Get New Stuff' only half-applies (+ the Kvantum fake-success trap)

Environment: Kubuntu 26.04 LTS · KDE Plasma 6 · Kvantum (qt-style-kvantum)

TL;DR

A KDE Global Theme is split into six pieces (colors, icons, cursor, window decoration, desktop theme, widget style), and "Get New Stuff" isn't guaranteed to push all of them into your system settings. Set the ones that didn't take with kwriteconfig6, and know that for the widget style (Kvantum), enabling the engine (widgetStyle=kvantum) is separate from picking a sub-theme.

The symptom: exactly half applied

The user installed and applied We10XOS-dark via System Settings → Appearance → Global Theme → "Get New Stuff," but it looked only half-changed to them. Comparing the screen they sent with the actual config files, exactly half had applied.

(That image isn't the user's screen — it's the example screenshot from the We10XOS-dark theme's own "Get New Stuff" listing, shown here as a reference for how the theme looks when fully applied.)

Diagnosis: this theme asks for six pieces

Opening the theme package's contents/defaults shows what it actually wants:

[kcminputrc][Mouse]      cursorTheme=Win10OS-cursors
[kdeglobals][General]    ColorScheme=We10XOSDark
[kdeglobals][Icons]      Theme=We10X
[kdeglobals][KDE]        widgetStyle=kvantum
[kwinrc][org.kde.kdecoration2]  theme=__aurorae__svg__We10XOS-dark
[plasmarc][Theme]        name=We10XOS-dark

But in the real config files, only colors (ColorScheme) and icons (Icons) had applied — cursor, window decoration, desktop theme, and widget style were all still default. "Get New Stuff" installs the package, but sometimes only pushes some of it into the live settings.

Fix 1: the three whose files already exist just need re-selecting

Cursor, window decoration, and desktop theme already had their files on disk (~/.local/share/plasma/desktoptheme/…, ~/.local/share/aurorae/themes/…, etc.) — they just weren't "selected" in the settings. I asked the user to write them directly with kwriteconfig6.

kwriteconfig6 --file kcminputrc --group Mouse --key cursorTheme Win10OS-cursors
kwriteconfig6 --file kwinrc --group "org.kde.kdecoration2" --key library org.kde.kwin.aurorae
kwriteconfig6 --file kwinrc --group "org.kde.kdecoration2" --key theme __aurorae__svg__We10XOS-dark
kwriteconfig6 --file plasmarc --group Theme --key name We10XOS-dark

Window decoration applies immediately with qdbus6 org.kde.KWin /KWin reconfigure, but cursor, desktop theme, and widget style only fully apply after a re-login.

Fix 2: the widget style (Kvantum) needs installing from scratch

Kvantum wasn't installed at all. The package name is a trap too — on Ubuntu 26.04 it's not kvantum but qt-style-kvantum.

sudo apt install qt-style-kvantum qt-style-kvantum-themes

And the We10XOS-dark Kvantum sub-theme isn't in the "Get New Stuff" package — it lives separately in the author's GitHub repo (yeyushengfan258/We10XOS-kde). Clone it, grab the Kvantum folder, install.

git clone https://github.com/yeyushengfan258/We10XOS-kde.git
mkdir -p ~/.config/Kvantum
cp -r We10XOS-kde/Kvantum/We10XOS-dark ~/.config/Kvantum/
kwriteconfig6 --file kdeglobals --group KDE --key widgetStyle kvantum

The misdiagnosis: don't trust Kvantum Manager saying "applied"

Here's the real trap. Kvantum Manager showed "Active theme: We10XOS-dark" at the bottom, and I took that as "done." That was wrong.

Why: Kvantum Manager's "active theme" only decides which sub-theme the Kvantum engine uses. Separately, whether apps use the Kvantum engine at all is a system setting (widgetStyle in kdeglobals) — and checking it, it had reverted at some point from kvantum to Windows (Qt's built-in style). Most likely the "Windows" entry in System Settings' Application Style list got clicked by mistake, confused with the theme name (We10XOS = "Windows 10").

kwriteconfig6 --file kdeglobals --group KDE --key widgetStyle kvantum

So to check the widget-style state, look at both Kvantum Manager's active theme and whether System Settings → Application Style is set to "Kvantum."

Takeaways / checklist

• A KDE Global Theme is six pieces, and "Get New Stuff" isn't guaranteed to apply them all — verify each by eye after a re-login.
• Kvantum's "pick a theme" and "enable the engine" are separate settings. If the widget style looks off, check both Kvantum Manager and System Settings' Application Style.
• On Ubuntu 26.04 the Kvantum package is qt-style-kvantum (+ qt-style-kvantum-themes).