public IList<CIMStringMap> CustomProperties {get; set;}

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D coord2D = new Coordinate2D(2.0, 10.0);

//Reference a point symbol in a style
StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
         .FirstOrDefault(item => item.Name == "ArcGIS 2D");
SymbolStyleItem symStyleItm = stylePrjItm.SearchSymbols(
                      StyleItemType.PointSymbol, "City Hall")[0];
CIMPointSymbol pointSym = symStyleItm.Symbol as CIMPointSymbol;
pointSym.SetSize(50);

var elemInfo = new ElementInfo()
{
  CustomProperties = new List<CIMStringMap>() {
     new CIMStringMap() { Key = "Key1", Value = "Value1"},
     new CIMStringMap() { Key = "Key2", Value = "Value2"}
   },
  Anchor = Anchor.TopRightCorner,
  Rotation = 45.0
};

var graphic = GraphicFactory.Instance.CreateSimpleGraphic(
                              coord2D.ToMapPoint(), pointSym);

ElementFactory.Instance.CreateGraphicElement(
  container, graphic, "New Point", true, elemInfo);

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D ll = new Coordinate2D(1, 1);
Coordinate2D ur = new Coordinate2D(4, 4);
Envelope env = EnvelopeBuilderEx.CreateEnvelope(ll, ur);

var tableFrameInfo = new TableFrameInfo()
{
  MapFrameName = mapFrameName,
  MapMemberUri = uri
};
var attribs = new List<CIMStringMap>();
for (int i = 1; i < 6; i++)
{
  attribs.Add(new CIMStringMap
  {
    Key = $"Key {i}",
    Value = $"Value {i}"
  });
}
var elemInfo = new ElementInfo()
{
  CustomProperties = attribs
};
var tableFrameElem = ElementFactory.Instance.CreateMapSurroundElement(
                              layout, env.Center, tableFrameInfo,
                              "New Table Frame", false, elemInfo) as TableFrame;