map.js

layer = await this.getWmtsLayer(); // some TileLayer from a WMTS source
google = new GoogleLayer({mapTypeId: "terrain"});
this.map = new Map({
  interactions: defaults({constrainResolution: true}),
  target: "map",
  layers: [google, layer],
  view: new View({
    center: this.project_info.center,
    zoom: 14
  })
});

let olGM = new OLGoogleMaps({
  map: this.map,
  watch: {
    tile: false
  }
});
olGM.activate();