The implication appears to be that going forward, M'Baku will rule as king of Wakanda, while Shuri will still be Black Panther, and he's presumably seeking the throne with her permission.

made his cinematic debut in Marvel Studios Black Panther (2018). He was a Wakandan by birth but was abandoned after his father's death at the hands of King T'Chaka due to betrayal of the throne.

Marvel Studios has released the official trailer for "Black Panther". The film features Chadwick ... must succeed to the throne of the technologically advanced African country of Wakanda.