public static IReadOnlyList<GraphicElement> GetElementsAsFlattenedList( 
   GraphicsLayer graphicsLayer
)

{
  var elements = graphicsLayer.GetElementsAsFlattenedList()
                      .Where(e => e.Name.StartsWith("Text"));
  // Note: must be called on the QueuedTask
  {
    graphicsLayer.SelectElements(elements);
    //or select one element
    graphicsLayer.SelectElement(elements.FirstOrDefault());
  }
}

{
  // Note: must be called on the QueuedTask
  {
    //Find elements by name
    var elems = graphicsLayer.FindElements(new List<string>() { "Point 1", "Line 3", "Text 1" });
    //Find elements by type
    //Find all point graphics in the Graphics Layer
    var pointGraphics = graphicsLayer.GetElementsAsFlattenedList().Where(elem => elem.GetGraphic() is CIMPointGraphic);
    //Find all line graphics in the Graphics Layer
    var lineGraphics = graphicsLayer.GetElementsAsFlattenedList().Where(elem => elem.GetGraphic() is CIMLineGraphic);
    //Find all polygon graphics in the Graphics Layer
    var polygonGraphics = graphicsLayer.GetElementsAsFlattenedList().Where(elem => elem.GetGraphic() is CIMPolygonGraphic);
    //Find all text graphics in the Graphics Layer
    var textGraphics = graphicsLayer.GetElementsAsFlattenedList().Where(elem => elem.GetGraphic() is CIMTextGraphic);
    //Find all picture graphics in the Graphics Layer
    var pictureGraphic = graphicsLayer.GetElementsAsFlattenedList().Where(elem => elem.GetGraphic() is CIMPictureGraphic);
  }
}

{
  var all_text = graphicsLayer.GetElementsAsFlattenedList()
                .Where(e => e.GetGraphic() is CIMTextGraphic);
}