Is there any work towards that upstream? If you are interested, there exists a Qt6-based lightdm-greeter variant that is more tightly coupled with libplasma and KF6: https://invent.kde.org/plasma/lightdm-kde-greeter
I've just been following the progress of this PR since the mailing list post as I've been prioritising fixing other more important issues in my TODO list first. As things stand, the qt5 USE flag just enables some features that will allow a qt5 greeter to run, however we don't have QT greeter in our repos so we could just drop the USE and depends for now, then revisit this when a standard (for lack of a better word) QT6 greeter emerges in lightdm community.
