Essentially some oldfashioned / ES6 module usage improvements. Notably, the ES6 module code is again available in a convenient way in the https://www.npmjs.com/package/olcs package. For oldfashioned builds, if you need to access internal OpenLayers APIs you can use https://github.com/geoblocks/legacylib/tree/master/ol5 to build a full version of OpenLayers.