Stylix's qt target sets QT_STYLE_OVERRIDE=kvantum and writes qt6ct/qt5ct configs with style=kvantum. plasmashell/KWin crash with a fatal 'module kvantum is not installed' QML error because the kvantum Qt style plugin is not available in the Plasma session. - stylix: targets.qt.enable = false (stops QT_STYLE_OVERRIDE=kvantum) - plasma: remove kvantum package, add widgetStyle=Breeze as belt-and-suspenders