Hi David,
I finally got around to the binary install of Qt 5.12.12 as you suggested, and attempted to build VTK-8.2.0 with module_vtkGUISupportQtOpenGL. I get a great number of errors in the compilation of QVTKOpenGLNativeWidget.cxx, again related to QOpenGLFunctions_3_2_Core. There seems to be an incompatibility, related to OpenGL 3. Time to give up, I think.
Best regards,
Gib