Is asking Shafa’ah from the prophet صلى الله عليه وسلم at his grave major shirk? I am confused because the prophet صلى الله عليه وسلم will do shafa‘ah on the day of judgement in sha Allah

You ask it from Allah، the Messenger does not do shafa'ah from himself he goes and prostrates to Allah until Allah lets him so he does not own it u ask Allah for it. Also asking shafa'ah is du'a' and du'a' is worship the moment we dedicated to other than Allah or associate someone else with him this is major shirk that as the ulama have stated.