Upgrading to MacOS Mojave resulted it "Panic Reports" (Black Screen Of Death) for my application build upon QGraphicsView and QOpenGLWidget.
Attached is a test project, uncomment the creation of a QOpenGLWidget for viewport.
I have tested this in 5.6.4, 5.10 and 5.12 (from today) all compiled with "-opengl Desktop" If that is of importance.
Update: Creating stand-alone QOpenGLWidget works as expected.
I was able to show QOpenGLWidget as viewport on screen by late-assigning it as such. This is, the widget and the view are first created, but only after they are shown on screen I call setViewport(widget). Sadly, if I try to resize the view I trigger a panic. Interestingly, before it is made a viewport, I can resize the widget to the size of the view.