public static IReadOnlyList<Element> GetSelectedElements( 
   GraphicsLayer graphicsLayer
)

{
  // Note: must be called on the QueuedTask
  {
    graphicsLayer.RemoveElements(graphicsLayer.GetSelectedElements());
  }
}

{
  //unselect the first element in the currently selected elements
  var elem = graphicsLayer.GetSelectedElements().FirstOrDefault();
  // Note: must be called on the QueuedTask
  {
    if (elem != null)
      //Unselect one element
      graphicsLayer.UnSelectElement(elem);

    //unselect all elements
    graphicsLayer.UnSelectElements();
    //equivalent to
    graphicsLayer.ClearSelection();
  }
}

{
  ArcGIS.Desktop.Layouts.Events.ElementEvent.Subscribe((args) =>
  {
    //check if the container is a graphics layer - could be a Layout (or even map view)
    if (args.Container is ArcGIS.Desktop.Mapping.GraphicsLayer graphicsLayer)
    {
      //get the total selection count for the container
      var count = args.Elements.Count();
      //Check count - could have been an unselect or clearselect
      if (count > 0)
      {
        //this is a selection or add to selection
        var elems = graphicsLayer.GetSelectedElements();
        //TODO process the selection...
      }
      else
      {
        //This is an unselect or clear selection
        //TODO process the unselect or clear select
      }
    }
  });
}

{
  // Note: must be called on the QueuedTask
  {
    var elemsToGroup = graphicsLayer.GetSelectedElements();
    //group  elements
    groupElement = graphicsLayer.GroupElements(elemsToGroup);
  }
}

{
  // Note: must be called on the QueuedTask
  {
    var selectedElements = graphicsLayer.GetSelectedElements().ToList(); ;
    if (selectedElements?.Count == 0)//must be at least 1.
      return;
    var elementsToUnGroup = new List<GroupElement>();
    //All selected elements should be grouped.
    if (selectedElements.Count() == selectedElements.OfType<GroupElement>().Count())
    {
      //Convert to a GroupElement list.
      elementsToUnGroup = selectedElements.ConvertAll(x => (GroupElement)x);
    }
    if (elementsToUnGroup.Count() == 0)
      return;
    //UnGroup
    graphicsLayer.UnGroupElements(elementsToUnGroup);
  }
}

{
  // Note: must be called on the QueuedTask
  {
    //get the current selection set
    var sel_elems = graphicsLayer.GetSelectedElements();
    //can they be brought forward? This will also check that all elements have the same parent
    if (graphicsLayer.CanBringForward(sel_elems))
    {
      //bring forward
      graphicsLayer.BringForward(sel_elems);
      //bring to front (of parent)
      //graphicsLayer.BringToFront(sel_elems);
    }
    else if (graphicsLayer.CanSendBackward(sel_elems))
    {
      //send back
      graphicsLayer.SendBackward(sel_elems);
      //send to the back (of parent)
      //graphicsLayer.SendToBack(sel_elems);
    }
  }
}

{
  // Note: must be called on the QueuedTask
  {
    var selElementsZOrder = graphicsLayer.GetSelectedElements();
    //list out the z order
    foreach (var elem in selElementsZOrder)
      System.Diagnostics.Debug.WriteLine($"{elem.Name}: z-order {elem.ZOrder}");
  }
}

{
  // Note: must be called on the QueuedTask
  {
    //Each selected element will move to a set distance to the upper right.
    var selElements = graphicsLayer.GetSelectedElements();
    if (selElements.Count == 0) return;
    //Move the element up
    foreach (var selElement in selElements)
    {
      //Get the element's bounds
      var elementPoly = PolygonBuilderEx.CreatePolygon(selElement.GetBounds());
      //get the coordinates of the element bounding envelope.
      var pointsList = elementPoly.Copy2DCoordinatesToList();
      //Move the element's Anchor point to the upper right.
      selElement.SetAnchorPoint(pointsList[1]);
    }
  }
}