It’s not just what became East Germany. People of all levels in Poland and the other countries who were under the Soviet sphere knew they were screwed. They were ignored.
Unfortunately Russia was already in Poland. Not much anyone could do about that. They were going to do what they were going to do. But Berlin and its surroundings, especially to the west, was up for grabs and through negotiations at Quebec and Yalta, FDR let Stalin have it. Other than Churchill and Patton, I don’t read of a whole of others who were howling in protest over that.