https://lxqt-project.org/

lxqt > Plasma > Deepin

More serious answer, Trinity.

But you're also setting up a bit of a false scenario because there are far more gtk DEs than what you have listed. Mate, Cinnamon, Budgie...

There are a few not-so-popular-yet options for QT based desktops out there.

I think LXQT fills the role of XFCE well.

And for an LXDE equal thing you could look at something like PaperDE or even DesQ although they are very early days still.

I don't know how active it is anymore and how stable on Desktop, but maybe Lomiri?

Deepin also seems similar, in that it seems to sit between the two, but I can't recommend that due to the persistent disregard of security issues re that DE.

Lumina was something a bit similar to XFCE in that it seemed to want a simple stable base and ui, with only key technologies updated, and lots of options. Looks dead though now, which is a shame as I enjoyed using it for BSDs.

Hmm what are you searching for specifically?

I think no other Qt baded, Wayland-capable DE exists, and thats probably okay.

I see though, how buggy and complex KDE sometimes is. KDE 6.0 will be more streamlined and unified, and I think on that base it cooould make sense to remove components, slim it down more, maybe prefer some resource saving Apps over others, and you are good to go.

At the same time I have no idea what apps should be replaced, as KDEs are very good. And with Trinity, based on some outdated version of KDE, I dont think you will get a good experience.