“Dissolve Verteces” will get rid of the verteces, but keep the surface, so the remaining verteces are connected through a face afterwards. After you delete the verts you have a single ngon where the geometry used to be. After that you extrude the verteces, but you don’t create new faces. So what you’re left with is an ngon that you don’t need and edges that are not filled with faces.
What should I choose instead of “dissolve verteces” when deleting verts?
Just regular delete verteces.