He feels like he isn’t fit to be the “King of Asgard”, so he’s been going down a more non-formal path since Odin died and he lost his hammer.
Plus, the Endgame writers said they worked closely with Chris Hemsworth in writing in his character. He has stated he was bored with his character after Dark World and Age it Ultron, and the Ragnarok version of Thor made him excited about the character again. So there’s that.