[Machine] I have never seen the Messenger of Allah ﷺ give a sermon while sitting on the pulpit on Fridays. So whoever told you that he sat, then they have lied. He used to give a sermon standing, then sit, then stand again to give another sermon, and he would sit in between the two sermons.
مَا رَأَيْتُ رَسُولَ اللهِ ﷺ يَخْطُبُ قَطُّ فِي الْجُمُعَةِ إِلَّا قَائِمًا فَمَنْ حَدَّثَكَ أَنَّهُ جَلَسَ فَكَذِّبْهُ فَإِنَّهُ لَمْ يَفْعَلْ قَالَ جَابِرٌ كَانَ النَّبِيُّ ﷺ «يَخْطُبُ ثُمَّ يَقْعُدُ ثُمَّ يَقُومُ فَيَخْطُبُ وَكَانَ يَخْطُبُ خُطْبَتَيْنِ يَقْعُدُ بَيْنَهُمَا»