GeoNetwork 4.0.3 release is a minor release with some changes:
Interactive graphics for facets (See Interactive graphics)
Indexing / Improvements, better multilingual support and more robust
Translation pack builder for faster initialization of the client application.
and more … see 4.0.3 issues and pull requests for full details.
Version 4.0.3 is also the version to use if testing the draft OGC API Records service.