Is joking by saying, "The room might clean itself one day" in response to a mother's request to clean the room considered a forbidden form of joking?

If the mother is not angered by this statement, then there is no harm in it as a joke, because it does not involve anything forbidden, with the caveat to be moderate in joking and not to overdo it. Joking is for the purpose of entertaining companions and showing affection to those one interacts with, or to dispel boredom and worry, as Al-Mawardi said. It was said to Ibn Sa'id ibn al-'As: "Be moderate in your joking, for excessive joking diminishes splendor and emboldens the foolish against you, while being deficient in it drives away your companions and makes your associates feel alienated from you."