Qt XpmCreateDataFromPixmap failing

Coming from https://forum.xfce.org/viewtopic.php?pid=76220 and https://github.com/user-none/KDocker/issues/128#issuecomment-2225953166 ...

It seems that Xfce is failing when applications use

https://man.archlinux.org/man/extra/libxpm/XpmCreateDataFromPixmap.3.en

which is part of the Freedesktop library libxpm. KDocker in that case is using https://doc.qt.io/qt-5/qicon.html#fromTheme