Using Scene3D component with RenderSettings' renderPolicy set to RenderSettings.OnDemand results in a high CPU usage on a still scene. When Qt3DQuickWindow is used instead, the issue is not there.

The high CPU usage when Scene3D is used can be tested with the official example simplecustommaterial, but you will need to add `renderPolicy: RenderSettings.OnDemand` in SceneRoot's RenderSettings.

For comparison, try the simple-qml example with the same OnDemand setting — it shows low CPU usage when using Qt3DQuickWindow.

I also tried with a custom built Qt 6.8.2 with -DFEATURE_qt3d_rhi_renderer=ON and explicitly using RHI with metal