Is holding mawlids for saints based on dreams and visions, as happened with the sheikh who requested in a dream that a mawlid be held for him, permissible in Islamic law? And what are the Shar'i proofs for that?

Holding Mawlid celebrations is among the blameworthy innovations. Healing comes only from Allah alone, and seeking healing from other than Allah is shirk (polytheism). The stories and dreams narrated in this regard are either lies or from Satan to mislead the ignorant. Satan may fulfill the need of one who seeks help from creatures, or he may appear to him in the form of the one he sought help from, so that the person considers it a miracle.