The Prophet ﷺ said: “Prolonging the prayer and shortening the sermon of a man is a sign of his understanding; so make the prayer long and the sermon short — for some speech is (like) magic.” (Muslim). ʿAmmār said: “I heard the Messenger of Allah ﷺ command us to shorten the sermon.”
العربية: عن عمّار بن ياسر رضي الله عنه قال: سمعتُ رسول الله ﷺ يقول: «إنّ طول صلاة الرجل وقِصَر خطبته مَئنّةٌ من فِقهه، فأطيلوا الصلاة واقصروا الخطبة، وإنّ من البيان لسحرًا». (مسلم).
Imams: keep the khuṭbah short and impactful — the Sunnah is a longer prayer and a shorter sermon.