kdsoap-qt6-devel installs CMake config files like
/usr/lib64/cmake/KDSoap/KDSoapConfig.cmake.

Manually building kdsoap against Qt6 however installs
/home/nico/kde6/usr/lib64/cmake/KDSoap-qt6/KDSoap-qt6Config.cmake etc. Note the
-qt6 infix.

This influences how the consumer is supposed to find the package. Therefore the
upstream code snippet
(https://github.com/KDAB/KDSoap/blob/kdsoap-2.1/INSTALL.txt#L97) doesn't work
on OpenSUSE.

As another consequence installing both kdsoap-devel and kdsoap-qt6-devel is not
possible:

Problem: the installed kdsoap-qt6-devel-2.0.0-2.2.x86_64 conflicts with
'kdsoap-devel' provided by the to be installed kdsoap-devel-2.0.0-2.2.x86_64
 Solution 1: deinstallation of kdsoap-qt6-devel-2.0.0-2.2.x86_64
 Solution 2: do not install kdsoap-devel-2.0.0-2.2.x86_64