​That works. It is even better when I put both H and I after it.

I also found a way to get resources at the correct place.

It know becomes:
    #+BEGIN_SRC dot :file test.png :cmdline -Kdot -Tpng
    graph {
      A
      B
      C
      utilities [label = "Utility's"]
   
      D
      E
      F [shape = rectangle]
   
   
      subgraph cluster_resources {
        color=blue
        resources [label = "Resources"]
      }
   
      G
      G_ [style="invisible"]
   
      K
      subgraph cluster_ta {
        color=blue
        {rank = same; L, M}
        L
        M
      }
      H
      I
   
      {rank = same; D,  E, F}
      {rank = same; G_, K}
   
   
      A -- F
      B -- F
      C -- F
      A -- D
      utilities -- resources [style="invisible"]
   
      E -- F
   
      F -- K
      F -- G
      F -- H
      F -- I
   
      G -- G_ [style="invisible"]
   
      K -- L
      K -- M
      L -- M
    }
    #+END_SRC

That looks very good indeed: I think I do not need to start working with ditaa. :-)