What does Jeremiah 46:21 mean?

Even her hired soldiers are helpless—they’re like fattened calves, but they’re turning and running away together. They can’t stand and fight, because the day of their disaster has come, the time for them to be punished. Jeremiah 46:21 - Modern Text Bible

(Egypt’s mercenaries, who were supposed to help, are useless. They’re fleeing because it’s the moment of Egypt’s downfall.)