Example of a Sphere Mollweide map with a Graticule layer. This demo is the same as the OpenLayers one but here, it uses the proj4rs library instead of the proj4js one.
proj4 OpenLayers
import GeoJSON from 'ol/format/GeoJSON.js';
import Graticule from 'ol/layer/Graticule.js';
import Map from 'ol/Map.js';
import Projection from 'ol/proj/Projection.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import proj4 from 'proj4';
import {register} from 'ol/proj/proj4.js';
...
proj4rs
import GeoJSON from 'ol/format/GeoJSON.js';
import Graticule from 'ol/layer/Graticule.js';
import Map from 'ol/Map.js';
import Projection from 'ol/proj/Projection.js';
import VectorLayer from 'ol/layer/Vector.js';
import VectorSource from 'ol/source/Vector.js';
import View from 'ol/View.js';
import {proj4} from 'proj4rs/proj4.js';
import {register} from 'ol/proj/proj4.js';
...