[Machine] I have never seen the Messenger of Allah ﷺ giving a sermon on Friday while sitting down. Whoever told you that he sat down, then he is lying. He did not do that. The Prophet ﷺ used to deliver his sermon standing, then sit down for a while, then stand up again and deliver another sermon. He used to deliver two sermons, sitting in between them on Fridays.
مَا رَأَيْتُ رَسُولَ اللهِ ﷺ قَطُّ يَخْطُبُ فِي الْجُمُعَةِ إِلَّا قَائِمًا فَمَنْ حَدَّثَكَ أَنَّهُ جَلَسَ فَكَذِّبْهُ فَإِنَّهُ لَمْ يَفْعَلْ كَانَ النَّبِيُّ ﷺ يَخْطُبُ ثُمَّ يَقْعُدُ ثُمَّ يَقُومُ فَيَخْطُبُ كَانَ يَخْطُبُ خُطْبَتَيْنِ يَقْعُدُ بَيْنَهُمَا فِي الْجُمُعَةِ