public CIMInternetServerConnectionBase ServerConnection {get; set;}

        // Create a connection to the WMS server
        var serverConnection = new CIMProjectServerConnection
        { 
  URL = "URL of the WMTS service.xml",
            ServerType = ServerType.WMTS,
        };
        var service_connection = new CIMWMTSServiceConnection { 
  ServerConnection = serverConnection,
            LayerName = "AdminBoundaries", // Specify the layer name you want to add
        };
        
        // Add a new layer to the map
        var layerParams = new LayerCreationParams(service_connection);
        layerParams.MapMemberPosition = MapMemberPosition.AddToBottom;
var map = MapView.Active.Map;
        await QueuedTask.Run(() =>
        {
            var layer = LayerFactory.Instance.CreateLayer<FeatureLayer>(layerParams, map);
        });