public static MapPoint CreateMapPoint( 
   double x,
   double y,
   double z,
   double m,
   SpatialReference spatialReference
)

// Use a builder convenience method or use a builder constructor.

// Builder convenience methods don't need to run on the MCT.
// create a 3d point with M
MapPoint pt = MapPointBuilder.CreateMapPoint(1.0, 2.0, 3.0, 4.0);

MapPoint ptWithM = null;

// Builder constructors need to run on the MCT.
ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
{
  using (MapPointBuilder mb = new MapPointBuilder(1.0, 2.0, 3.0, 4.0))
  {
    // do something with the builder

    ptWithM = mb.ToGeometry();
  }
});

MapPoint clone = ptWithM.Clone() as MapPoint;
MapPoint anotherM = MapPointBuilder.CreateMapPoint(ptWithM);