i want to display a simple Cube created from MapPoints for a SceneView. (i know there is a Symbol called SimpleMarkerSceneSymbolStyle.Cube) But i want to create a geomtery out of this points.
Is the correct way to use PolygonBuilder?
You have a couple of options. You can use a Polygon and use extrusion on the renderer to extrude it to a box.
Or you can use a model symbol, and use a 3D Model that's a cube together with a point symbol (but that's essentially equivalent to the approach you mention).
Creating actual meshes on the fly isn't supported at this point.