Vini and Mbappe do not play in the same position, in the case that Mbappe is in Real Madrid, there is little chance of Vinicius Jr. leaving Real Madrid. Vinicius Jr. has received a big offer from Manchester United before but Junior directly turned down the offer from Manchester United as he started his career at Real Madrid and will end his career at Real Madrid if Real Madrid do not sell him. Vinicius Jr plays as a winger for Real Madrid, on the contrary, if Mbappe joins Real Madrid, he will play as a finisher. We are only saying this but the club knows very well what will be decided on this matter and we may know the official news at the end of certain period.
Mbappe can play in Vini's position, but he can also play as a central striker. He can play in some positions, which makes him very dynamic depending on what strategy the team implements. For example, when Enrique ordered him to play as a central striker, Mbappe was doing it.
The same thing can also happen in real madrid when the club doesn't have someone who can play as a number nine. mbappe can fulfill this position that is currently filling by joselu. There is no problem when Mbappe is placed as a central striker under Ancellotti caused by Mbappe is very capable of doing it.
Mbappe is very flexible, which makes him different from the other players. He can play in various positions, which is really helpful when the club needs an urgent striker to play at the bottom.