Hello. A friend was curious about the 3DGS engine and wants to know if it has the ability to do Cell-shading. Is this possible?

Yes...

You can either "fake it" by copying the model, inverting the faces, and scaling it slightly larger.

OR, you can simply use a shader that does this for you, and even better. However, this requires Comm or Pro editions...

hey Guitar , i didn't hear about that with render to texture (I guess: because it needs comm or pro).Can you tell me what effect it produces?
And what are the adventages?

You don't need render_to_texture

You simply use a two-pass shader. The first renders the model normally, and the second renders it:
- black
- reversed culling [inversed normals]
- slightly expanded