I've encountered the following line in /usr/lib64/cmake/Qt6Gui/Qt6GuiDependencies.cmake set(_Qt6Gui_MODULE_DEPENDENCIES "Core;DBus") Because of this line, any project requiring Qt6Gui as a cmake dependency will fail to comple because dbus is missing. I wonder - is this a cmakeism, or does Qt6Gui require Qt6DBus in runtime as well?
Nevermind, this cmake dependency is controlled by USE=dbus. Any package that optionally depends on QtDBus will need to propagate that flag with dev-qt/qtbase:6[dbus=]