I found out from Wikipedia:
Croatia's accession to the EU obliges them to apply for membership in the European Economic Area (EEA). The Croatian government submitted their application on 13 September 2012, and membership negotiations started 15 March 2013 with the aim to enlarge both the EU and the EEA on the same date, 1 July 2013. However, this was not achieved. On 11 April 2014, the EU and its member states (including Croatia), Norway, Iceland and Liechtenstein signed an agreement concerning the accession of Croatia to the EEA. It is yet to be ratified, but is provisionally applied with regards to Croatia. As of March 2022, the agreement has been ratified by 23 out of 31 parties.
The list of countries that haven't ratified Croatia's accession to the EEA also seems pretty weird. E.g. France is on that list, but the French Senate and their National Assembly had unanimously ratified Croatia's accession to the EU. (The same goes for Cyprus' parliament.) So, what are the causes for this long delay in Croatia's accession to the EEA?