3D objects that each form a 3D scene can be combined into a single 3D scene.
Insert a 3D object from the 3D Objects toolbar (for example, a cube).
Insert a second slightly larger 3D object (for example, a sphere).
Select the second 3D object (sphere) and choose Edit - Cut.
Double-click the first object (cube) to enter its group.
Choose Edit - Paste. Both objects are now part of the same group. If you want, you can edit the individual objects or change their position within the group.
Double-click outside the group to exit the group.
You cannot intersect or subtract 3D objects.