Did the build/install of Geant4 itself have Qt support enabled (i.e. -DGEANT4_USE_QT=ON)? If it did, what /vis/open command, if any, is called in any macro(s) being run?
If you use the CMake GUI, then it should appear as an option there that can be ticked to enable it. Provided Qt5 is installed in a standard way, it should pick things up.
Note that this does require a rebuild/install of the Geant4 itself, and then the application to be rebuilt to pick up that changes.