Near the end of Black Panther: Wakanda Forever, in the Wakandan challenge/enthronement ceremony, after Princess Shuri was introduced, it is M'Baku who comes out of the ship instead.
M'Baku: The Black Panther sends her regards, but she will not be joining us today. I, M'Baku, leader of the Jabari Tribe, son of Wakanda, wish to challenge for the throne.
The scene cuts off after the above dialogue was said.
(The scene seems to be a callback to the humorous scene in Black Panther where the crowd was asked who wanted to challenge T'Challa. Shuri raised her hand, surprising everyone, but she just jokes that her corset is uncomfortable and that they should all just wrap it up and go home.)
Due to the absurdity of M'Baku's entrance and challenge (and seemingly mirroring what Shuri did in Black Panther), I'm not sure if M'Baku's challenge was also meant to be humorous, if M'Baku was just kidding.
Since Shuri wasn't present in the ceremony, M'Baku will have no one to fight for the challenge. What is the significance of M'Baku's challenge? By not presenting herself in the ceremony, did Shuri turn over the throne to M'Baku? Or is it just a joke by M'Baku?