My solution for now.

Though the better option would be to include the library config in the plugin.

(https://www.outsystems.com/forums/discussion/22609/idea-way-to-load-google-maps-libraries/)

eSpace: GoogleMapsMobile

====================================

Action: GoogleMaps/Map/API_LoadGoogleAPI

Description: Activated the drawing library in the config in order to be able to use it.

// Ensure Libraries are loaded (but only once)
if(typeof google === 'undefined') {
    require.config({
        paths: {
            googlemaps: $parameters.GoogleMapsScriptURL ,
            async: $parameters.ASyncScriptURL
        },
        googlemaps: {
            params: {
                key: $parameters.ApiKey,
                libraries: 'drawing'
            }
        }
    });
    require(['googlemaps!'], apiInitializeFinish);
} else {
    $actions.InitMap();
}

Script: OsGoogleMap.js

Function: Create

Description: Added the part in red which probably could also be added after the map has been created outside the plugin.

// Function that creates the maps
    this.create = function(mapId, containerId, zoom, center, mapOptions, callback) {
       
        var containerEl = document.getElementById(containerId);
        var mapOptionsRequired = {};
       
        if(typeof containerEl !== 'undefined'|| containerEl !== null){
           
            mapOptionsRequired = {};
            mapOptionsRequired = {zoom: parseInt(zoom) || 8};
           
            //If center exists add it to the map options
            if(center){
                mapOptionsRequired = {zoom: parseInt(zoom) || 8, center: center};
            }
           
            var opts = gmapExtend({}, mapOptionsRequired, mapOptions);
       
            var map = new googleMaps.Map(containerEl, opts);
           
            var drawingManager = new googleMaps.drawing.DrawingManager({
                drawingMode: googleMaps.drawing.OverlayType.MARKER,
                drawingControl: true,
                drawingControlOptions: {
                  position: googleMaps.ControlPosition.TOP_CENTER,
                  drawingModes: ['marker', 'circle', 'polygon', 'polyline', 'rectangle']
                },
                markerOptions: {icon: 'https://developers.google.com/maps/documentation/javascript/examples/full/images/beachflag.png'},
                circleOptions: {
                  fillColor: '#ffff00',
                  fillOpacity: 1,
                  strokeWeight: 5,
                  clickable: false,
                  editable: true,
                  zIndex: 1
                }
            });
            drawingManager.setMap(map);
           
            google.maps.event.addListenerOnce(map, 'idle', function(){
                if(typeof callback === 'function'){
                    callback();
                }
            });
           
            google.maps.event.addListener(map, 'bounds_changed', function() {
                google.maps.event.trigger(map, 'resize');
            });
           
            return newMap(mapId, containerId, map);
        }
    };

Result: