public void ExportScene3DObjects( 
   ExportSceneContentsFormat exportFormat
)

{
  //Export the map view associated with a map frame to BMP.
  string filePath = @"Path and file name for the output export file";
  //Create BMP format with appropriate settings
  //EMF, EPS, GIF, JPEG, PDF, PNG, SVG, TGA, and TFF formats are also available for export
  BMPFormat BMP = new BMPFormat()
  {
    Resolution = 300,
    Height = 500,
    Width = 800,
    HasWorldFile = true,
    OutputFileName = filePath
  };

  //Export on the worker thread
  await QueuedTask.Run(() =>
  {
    MapView mv_bmp = mapFrame.GetMapView(layoutView);
    if (mv_bmp != null)
    {
      //Check to see if the path is valid and export
      if (BMP.ValidateOutputFilePath())
      {
        mv_bmp.Export(BMP);  //Export to BMP
      }
    }
  });
}

{
  // Validate the current active view. Only a local scene can be exported.
  bool CanExportScene3DObjects = MapView.Active?.ViewingMode == MapViewingMode.SceneLocal;
  if (CanExportScene3DObjects)
  {
    // Create a scene content export format, export the scene context as a glTF file
    var exportFormat = new ExportSceneContentsFormat()
    {
      Extent = mapView.Extent, // sets Extent property
      FolderPath = @"C:\Temp", // sets FolderPath property
                               //sets FileName property.The export format is determined by the output file extension (e.g.,.stl, .gltf)
      FileName = "my-3d-objects.gltf",
      IsSingleFileOutput = true, // sets whether to export to one single file
      SaveTextures = true //sets whether to save textures
    };
    // Export the scene content as 3D objects
    mapView.ExportScene3DObjects(exportFormat);
  }
}