It has zilch to do with any sort of one China policy. You made a link that is not there. The Potsdam Declaration does not even deal with the Allies’ relationship with the Republic of China. It simply states that Japan will surrender and retreat from the territories they invaded. Please point out what lines in either the Potsdam Declaration or the Cairo Declaration that have anything to do with the Allies’ relationship with the Republic of China. Both deal with the Allies’ relationship and demands from Japan at the time.