Some housekeeping is not done when you don’t use runRenderLoop (engine.beginFrame / engine.endFrame are not called for eg). Also, the multi views (canvas) support won’t work, as well as VR as I can see there are some calls to VR functions in the engine._renderLoop wrapper.
So, not using runRenderLoop may work in your case but I’m not sure it is an officially supported way of doing things. @Deltakosh?
In any case, WebGPU needs at the minimum that beginFrame / endFrame be called: you can try to surround your scene.render() call by engine.beginFrame() and engine.endFrame() and see if that works.
For reference, here’s the render loop wrapper of Engine: