If you add a 2D model to a 2D scene, you can render it into a 2D layer. When you do that, you must decide from which angle and position the model is going to be rendered. After that, it becomes rasterized into a bitmap layer. Although the layer itself can be manipulated like a normal drawing layer, the object itself cannot be manipulated like a 3D object in the panel. The point of view from which it was rendered can be adjusted if needed, but such adjustments are made for the whole panel.
Although this approach is more limited, it can be preferable if you only need to use a 3D model as a reference or to make a static background, as creating a 2D scene is more simple than a 3D scene. If you need to be able to make 3D transformations or animations to your 3D models, you will need to convert your scene into a 3D scene and import your model as a 3D object—see About Adding 3D Models to 3D Scenes