Regarding the positions of Vini and Mbappe, it is indeed a difficult thing because both are good players but the problem is that they operate in the same position, which means that one of the players must be sacrificed to be rotated and occupy another position. And coincidentally the position needed is a center forward and Mbappe was shifted to center forward and the results have not been very satisfactory. He tried to experiment, but so far what he did has not been very successful. Actually I don't agree if the coach experiments in the middle of the competition, but I can understand that there are not many options for Ancelotti so he has to dare to make decisions, which currently do not look impressive, even tend to be disappointing.
Ancelotti signed Mbappe for a striker position. Mbappe must be aware that he must adapt for the new position. Ancelotti won't force Vini to play as a striker, Vini has a crucial role as a left winger in Real Madrid lineup. So, Mbappe actually has no choice, he must try to play as a striker as well as possible. If he fails to play as a striker, I think Real Madrid will prefer to sell Mbappe over Vinicius.