Australia and Turkey have not agreed on who will host the next COP, and the chosen region in which the two countries are located should decide. According to the rules of the United Nations body that deals with climate change, the host country of the United Nations Framework Convention on Climate Change, which is Germany, will host the Conference of the Parties, if no agreement is reached. But the person holding the presidency is not Germany, but the country that hosted the last Conference of the Parties.
According to the rules, Ambassador Andre Correa do Lago will already be president until next year, but if the impasse continues he will have to remain president for another two years.
Germany has already warned that the COP cannot be in Bonn because it is too small a city to host such a large event. In this case, the country will choose a larger city, perhaps Berlin.
Fun fact: The Turkish and German pavilions are located next to each other at the COP in Belem.