public void ExportScene3DObjects( 
   ExportSceneContentsFormat exportFormat
)

// Validate the current active view. Only a local scene can be exported.
bool CanExportScene3DObjects = MapView.Active?.ViewingMode == MapViewingMode.SceneLocal;
if (CanExportScene3DObjects)
{
  //Gets the active map view.
  MapView mapView = MapView.Active;
  // Create a scene content export format
  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);
}