Is there a way of overlaying kmz data on maps ??
kmz is a Google Earth keyhole markup archive as you are aware. A KMZ file consists of a main KML file and supporting files packaged using a Zip utility into one unit, called an archive. The kml is, in essence an xml file; app inventor can handle those. They can be awkwardly converted with code to a geojson file or a LineString (that can be used show a trak) or directly converted to a geojson Features file (see below).
There is no way to directly overlay kmz data on the OpenStreetMap tiles used by MIT's Map component. The kml needs to be converted to something the Map component can display.
The easiest way to work with a kmz I expect is to separate the zipped archive into its parts and work with the kml. There are online converters that convert the kml to a geojson file. The Map component uses a geojson to display Features ( map traks using the LineString, or Markers etc)
Another way to work with the kml is to manually extract geocoordinates and create a LineString to display the coordinates in a format compatible with the Map component.
Both of these are doable. What you do depends on what you expect to display and how the kml is formatted.
Regards,
Steve.