Unable to create a library override

Hi. I imported a heavy asset as a link. I would like to change the position of one of the meshes within the link, but when I pick the linked mesh and go to Object>Relations>Make a Library Override, it is greyed out.

Another curious aspect of it is that when I use “make instance real” and the mesh becomes editable, the file weights are almost the same.

The scene without the linked mesh is 6MB with the linked mesh is 1.1 GB and with the mesh converted to “real,” is 1.2 approx…Am I missing something here? What is the advantage of linking? Or maybe the reason for links is just viewport performance, but not the file size?

Thank you

Did you link a collection or a collection instance or an object?

Make instances real actually puts the real geometry in the scene file.