They use a shader effect round them out which is broken in Qt 6; see Bug 470599.
Nate advised to set this as confirmed.
Git commit 65e3986a0893888f14c092b93c0cd7f8d8f5b9a9 by David Redondo. Committed on 23/08/2023 at 16:55. Pushed by davidre into branch 'master'. Make shaders in lookandfeel compatible with Qt6 Because qt_add_shaders requires a target use a dummy one and add it to ALL. Unfortunately there seems to be no way to query the generated files so we rely on the fact that they are always generated in .qsb. Related: bug 470601 M +1 -1 CMakeLists.txt M +25 -0 lookandfeel/CMakeLists.txt A +51 -0 lookandfeel/org.kde.breeze/contents/components/UserDelegate.frag M +1 -39 lookandfeel/org.kde.breeze/contents/components/UserDelegate.qml A +22 -0 lookandfeel/org.kde.breeze/contents/components/WallpaperFader.frag M +1 -12 lookandfeel/org.kde.breeze/contents/components/WallpaperFader.qml https://invent.kde.org/plasma/plasma-workspace/-/commit/65e3986a0893888f14c092b93c0cd7f8d8f5b9a9