Selling Vinicius Jr. wouldn't solve the problems, because he's a top-quality player, and Real Madrid would be unlikely to find another player of his caliber. If they wanted to sign him, they'd have to pay a very high transfer fee. Therefore, Xabi Alonso must do his part to the best of his ability and maintain a balance between the players. In this case, the team wins.
Are you always willing to seeing Madrid to always rely upon him and his skill? If he performs well, that's acceptable what if he performs badly like the previous games? Come on man! Madrid needs more than one player to shine again. They're a club, and must be working as a team, not rely upon individual.
They can't have two suns in the same club . That's it.
Real Madrid never relies on a single player. They have vini, they have mbappe, they even have Jude, they have other players too. So that means, if anything happens to Vini, they should have other good enough players to understand as well. This has to be something that focuses on what to do and who they need, and they are never just "one person" team at all. That is the most important part and we shouldn't really focus on getting any one player to be that special.
However, that also doesn't mean that they need to sell him, why would you sell a good player when they have him already? They would need another player that is good, sure it wouldn't make them bad, but why bother selling one and getting another, that doesn't really get any better at all.