I wrote "predominant", not "official". And I think that is still true.
Also, from what I can tell using the site, it does not serve as a full dictionary. Rather, it lists the general rules of German orthography (as decided by the Rechtschreibrat) and has some limited tables of special words.
Since 2004 the official guidelines for the german speaking countries (Germany, Austria, Swiss, Belgium, South Tirol, Liechtenstein, Romania, Hungary - see this founding document with the list: https://www.rechtschreibrat.com/DOX/wiener_erklaerung.pdf) are covered by the Rechtschreibrat (https://www.rechtschreibrat.com/).
The official german dictionary is here: https://grammis.ids-mannheim.de/rechtschreibung/6774