The Duden is not official since 1996.

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