CINEMA 4D’s primitive objects and spline primitives are parametric, i.e., they have no points or polygons and are instead created using math formulae and parameters. Since these objects have no points or polygons, they can’t be edited in the same way as normal polygon objects and splines. For example, you can’t select and move points, nor can you apply commands like Extrude and Create Outline.
However, you can edit these objects if you first convert them to points and polygons. To do this, select the desired primitives and choose Mesh / Conversion / Make Editable.