I'm sorry.
Indeed, I was wrong in my example which leads to confusion (I am the first one).
grdMyStringGrid (my example uses a very bad "name") is, as the compiler tells me, a TDBGrid (which, in the VCL, is not at all on the same branch as TDrawGrid, TCustomGrid branching between the two in the VCL. But with Delphi "TDrawGrid(myDBGrid).Colwidths" compiles).
Anyway, knowing what is possible or not now, I will do it differently with Lazarus.