$ grep prefix /usr/lib64/pkgconfig/dtkgui.pc prefix=/usr exec_prefix=${prefix} libdir=${prefix}//usr/lib64 includedir=${prefix}/include/dtk5/DGui As results, all users of dtkgui.pc are broken, too. By the way, the name of this package is also wrong, it has to be called libdtkgui-devel instead.
Already fixed. The package was so named because the Qt5 on which it is based uses a similar name. If this doesn't give the right to violate the Library policy, then I will rename the package.