Theoretically, selling vinicius Junior to buy a striker and make kylian mbappé to play his natural wing which happens to be where vinicius junior is strongly occupying now is a good option. But in practice it is very very risky. I mean there is no club that is rich enough which will have someone like vinicius junior who is considered the best player in the world now and selling him just to make some unrealistic experiments.
They have already seen the gambling that Ancelotti did how it is playing out. There was actually no need to bringing kylian mbappé when vinicius Junior is there. But if your recommendation is taken by Real Madrid, it is a 50/50 thing. It could turn out to be the solution to Real Madrid problem or it could worsen it. There is possibility that it will worsen the problem than to redeem it because kylian mbappé will tend to be the new king which other players might disagree with him.
You are right selling Vinicius Junior to buy striker and moving Kylian Mbappé to his natural wing position might seem like good idea but it is very risky too. No team would want to sell player as good as Vinicius Junior who is considered one of best in world. Real Madrid has already seen unpredictable results from their experiments. Signing Mbappé might not have been necessary with Vinicius Junior already on team. If Real Madrid do this so it will lower chances of success and it could create tension among players if Mbappé becomes new star. This decision needs careful thought about potential risks and benefits.
It's very risky and I don't think they can take such a big risk. Maybe now they have to be more patient to wait for Mbappe to show his best performance as a center forward because this season he was only placed in that position and it takes a very long time to be able to adapt and play comfortably in that position. Vini is already comfortable playing for Real Madrid, and losing him to make Mbappe return to his original position is very risky, because we haven't seen Mbappe's contribution if he is played in his original position. So I think Real Madrid should be more patient.