QSGEngine? Not supported with the rhi path at the moment. What is the plan going forward? Not straightforward to offer a fix or replacement.
Who uses QSGEngine? Can it be removed in 6.0?
Based on https://code.woboq.org/qt5/qtdeclarative/src/quick/scenegraph/util/qsgengine.cpp.html#_ZN9QSGEngine10initializeEP14QOpenGLContext QSGEngine is not used by anyone. It perhaps used to be used by WebEngine but it has since migrated away (and uses QQuickWindow and QQuickWidget instead)