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

{
  //Note: 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(
    layout, graphic, "New Point", true, elemInfo);
}

{
  //Note: 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 = "Map Frame",
    MapMemberUri = "CIMPATH=USNationalParks/NationalParks.json"
  };
  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;
}