Comment # 27 on bug 920792 from Simon Lees

(In reply to Ludwig Nussel from comment #26)
> I just had a similar situation within 42.2. Suddenly dolphin, digikam etc
> had no icons anymore when run in WindowMaker. I thought this worked
> initially, so probably broke with some update. Not sure whether to recycle
> this bug but since it's still open...
> We need a proper solution that works out of the box for this. It's quite non
> obvious having to install qt5ct and run it once to make KDE applications
> look proper. So far qt5ct even interfered with a KDE session which made it
> even less acceptable (sr#492216).

Installing qt5ct is not required to fix the issue, you just need to set a
couple of environment variables so Qt falls back to something sensible if it
doesn't detect the desktop. For example enlightenment exports the following.

QT_QPA_PLATFORMTHEME=gtk2
QT_STYLE_OVERRIDE=gtk2

This meant that when running A Qt / KDE application under enlightenment it
would use the gtk based theming (enlightenment has a dialog to set the gtk
theme) while if I run under KDE it will use the kde theme. It would be nice if
Qt handled its fallback better so that it went to something like Fusion with a
icon theme if it didn't detect the desktop rather then picking nothing.

It seems like what I was doing above is broken with the latest Qt in
tumbleweed, I guess maybe the gtk fall back stuff has changed or something.
Unfortunatlly I just moved house and don't have a proper internet connection
and can't debug much further until I do.