The overlays work much the same way the base layer works. You need to find (or create) a tile source which takes /{z}/{x}/{y} in the url. Z being the zoom level for which you can define a min and max zoom level in the software factory.
Here is an example of a configured overlay:
 

Is this enough information or is there a specific problem you try to solve?

For future reference: If you want an overlay that looks like the ‘Truck-free zone’ in the docks, you can use data mappings instead of an overlay and create a polygon data mapping and feed it with waypoints through a view or table:

 Make sure that the map component uses a view or table that contains columns with coordinates in JSON for example:

{
    "CoordSets": e
         
            {
                "Lon": "6.932740",
                "Lat": "53.329700"
            },
            {
                "Lon": "6.932740",
                "Lat": "51.329700"
            },
            {
                "Lon": "8.932740",
                "Lat": "51.329700"
            },
            {
                "Lon": "8.932740",
                "Lat": "53.329700"
            },
        ]
    ]
}

and each row should contain a definition of the type of entity you want to display on the maps. You can make a domain with elements for this and select the element you would like to display on each row.

The two columns (coordinate and entity) should match the columns configured on your map component in the SF: 

Thank you Jitse,

We could make a work around with a data mapping instead of an overlay, but this is not the desired solution.

The overlay functionality is already available in the platform an should work I asume? 

@Erwin Ekkel could you ask someone from the development team to provide just a simple example of how to enable a overlay on a map, like the Truck-free zone?

This is our goal: (Overlay = Gray windmills, Data Mapping: Other Icons)