public static IReadOnlyList<Element> GetSelectedElements( 
   GraphicsLayer graphicsLayer
)

//on the QueuedTask      
graphicsLayer.RemoveElements(graphicsLayer.GetSelectedElements());

var graphicsLayer = MapView.Active.Map.GetLayersAsFlattenedList()
                    .OfType<ArcGIS.Desktop.Mapping.GraphicsLayer>().FirstOrDefault();
if (graphicsLayer == null)
  return;
//unselect the first element in the currently selected elements
var elem = graphicsLayer.GetSelectedElements().FirstOrDefault();
QueuedTask.Run( () => {
  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
    }
  }
});

var graphicsLayer = MapView.Active.Map.GetLayersAsFlattenedList()
                    .OfType<ArcGIS.Desktop.Mapping.GraphicsLayer>().FirstOrDefault();
if (graphicsLayer == null)
  return;

var elemsToGroup = graphicsLayer.GetSelectedElements();
//Note: run within the QueuedTask
//group  elements
var groupElement = graphicsLayer.GroupElements(elemsToGroup);

var selectedElements = graphicsLayer.GetSelectedElements().ToList(); ;
if (selectedElements?.Any() == false)//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);

//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);
}

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

//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]);
}