Right, I’m aware of the restrictions on the QVTKOpenGLWidget, but did not think QTabWidget was one of those circumstances. AFAIK it has no nested QScrollArea or similar inside it.
We have a couple of VTK widgets where we have to use the native widget (e.g. color/opacity settings, similar to Paraview’s situation).
…but, I’m actually pleasantly shocked, because upgrading to Qt 5.12.3 seems to have solved that particular problem I described above.
Still having some problem with another one of our VTK widgets on macOS though, the problem there being that the very first render seems to be a hit and miss (sometimes it works, sometimes it doesn’t, and a resize is necessary to get it back into shape).