Generally Rhino contains geometry (heavy data, lot of points, curves etc) and grasshopper is a light small file containing only code.
Inside grasshopper there are the params (like the “Brep” you used) which can cointain REFERENCED geometries , that is just a “link” to the actual rhino file geometries, not the geometry itself.
As you attached the .gh file only and not also the .3dm , it does not contain the geometries.
But, you can also save the geometries inside the param object.
You need to “internalize” your geometries (to save them inside the .gh file) in the Brep params.
See the video at point 3 here: How to ask effective questions
(Also, see that whole post…)