This is clear view on Vinicius Jr. future at Real Madrid. You believe he won't leave anytime soon especially with team doing well and building for future and if he ever does Madrid would demand huge transfer fee. And yes when he gets older he will likely move to Saudi Arabia for big salary as Real Madrid even like with Cristiano Ronaldo tends not to meet extremely high pay demands showing they value performance but have financial limits.
Vinicius can achieve anything at Real Madrid, and he's still very much needed by Xabi Alonso, making it impossible for him to leave the club anytime soon. Vinicius also has a contract with Real Madrid until 2027, and if any club wants him, they'll have to pay his very high release clause. Even if the Saudi Arabian League could do that because they have the money, I don't think Vinicius will take that opportunity.
Xabi Alonso is preparing for a new era at Real Madrid, and I think Vinicius will be a key part of that, so it's impossible for Xabi Alonso to let him leave easily. Next season, competition in La Liga and the Champions League will be even more intense, making Vinicius' presence crucial.