Thanks to Costanza Honorati and Laura Carpaneto for the tip!
The Practice Guide on the Brussels IIb Regulation (Regulation 2019/1111) has been published on the site of the European Judicial Network in Civil and Commercial Matters (EJN) – scroll to the bottom.
The Guide was written by Boriana Musseva under a contract between the European Commission and Milieu Consulting, under the supervision of the EJN. It uses the name Brussels IIb (presumably the Commission’s preferred nomenclature) even though some authors also use Brussels IIter. The Guide is still being translated in the other EU languages and will then also be published with the other information that the Commission provides on the European Judicial Atlas.
Here is the direct link to the Practice Guide for the application of the Brussels IIb Regulation.