The new kde5 and qt5 vcl plugins are not build with 6.2.0.3. See for example
the buildlog:

configure: VCLplugs to be built: gtk gtk3 gtk3_kde5

See also release notes:

> Two new VCL plugins (qt5 and kde5) have been implemented (with the KDE5 plugin extending the Qt5 one) to provide integration into KDE Plasma 5 and other Qt5-based desktop environments, mainly implemented by Katar�na Behrens (CIB) and Jan-Marek Glogowski (City of Munich).

Looking at the spec file first kde5 is enabled, but later in the file kde5 is
disabled again. I think qt5 also need to be enabled for kde5 to work.