Sure, but it never was — the .eu domain was for the European Union from the beginning, and the ISO code EU is for the European Union. The .eu domain was opened

Sure, but it never was — the .eu domain was for the European Union from the beginning, and the ISO code EU is for the European Union. The .eu domain was opened by agreement to the EEA (Iceland, Liechtenstein, Norway) countries as well. But Swiss registrants have never been eligible (except via citizenship/residency in one of the qualifying states), for example. When the UK left the EU, they didn't negotiate any EEA-style agreement to get access to .eu in their Brexit deal.