If Vini prioritizes his career as a footballer, then he will reject the offer. But if he prioritizes his career, then he will reject the offer. Because I think if he goes to the Saudi Pro League, then it is a step down from his career.
If he moves to Saudi league, he will miss UCL only. He still can have the chance to win domestic competitions and still can play in Brazilian national team. It is not too bad for his career even if he will play in a lower level of football competition. If he still wants to return to European leagues, he can sign for 3 years only. He is still young, I think it is not a too bad decision to grab the money and play for 3 years in Saudi league.

Real Madrid also get huge money if they accept the Saudi team offer. Real Madrid can buy again another star players. Real Madrid can buy Osimhen to play in CF (striker position) and Mbappe plays as LWF (left winger).
I don't mean to belittle Arab football, but right now Arab football and European football cannot be compared. He might also achieve individual achievements in Europe as you said.
Why we must compare Saudi league with European leagues? Sure, European leagues are higher level, everyone must understand it very well. It is true that to be the best player in the world, it is needed to play in European leagues. But the title of best player never gives huge money, Saudi teams can give bigger money although the league doesn't offer a better career.