Is the preacher sinful if he delivers a Friday sermon about our Messenger (peace and blessings be upon him) on the occasion of the Prophet's birthday, knowing that he deems celebrating the Prophet's birthday permissible?

It has been previously explained that celebrating the Prophet's birthday (Mawlid) is an innovation (bid'ah). Dedicating the Friday sermon to the Prophet every year, approximately around the time of the Mawlid, with the intention of drawing closer to Allah, falls under the category of forbidden innovations. This is unless it is done incidentally and for a specific purpose, without persistence or the belief in its virtue at that particular time, while also reminding people of the innovation of celebrating Mawlid and warning against it.