Which mode to use edit existing deck.gl polygons using nebula.gl?

Question

I'm trying to implement a basic example to edit GeoJSON polygon features using deck.gl. Layter I need to edit a lot of data, so I want to use nebula.gl, specifically EditableGeoJsonLayer.

My problem basically is that ModifyMode adds additional features instead of editing existing polygons:

onClick: (event) => {
    selectedFeatureIndex = event.object ? [event.index] : [];
    console.log(event.object, selectedFeatureIndex);

    deck.setProps({
      layers: [
        new EditableGeoJsonLayer({
          id: "geojson-layer",
          data: COUNTRIES,
          pickable: true,
          pickingRadius: 10,
          autoHighlight: true,
          mode: ModifyMode,
          selectedFeatureIndexes: selectedFeatureIndexes,
        }),
      ],
    });
  },

The whole example can be found here.

I'm just starting with nebula and have a problem of understanding the different modes which can be used with EditableGeoJsonLayer.

Just as a note, for now I use plain Javascript. I want to avoid React, as my app where I want to integrate it, runs on vue.js.