When this transfer took place Mbappe no longer attracts so much attention, instead they often start writing about how clubs from Saudi Arabia want to buy Vinicius, and perhaps this attracts so much attention because he has a clause of $1billion in his contract, but they are ready to pay it, and if it is true that they offered Vinicius a contract for €350m per year, this is a huge amount of money, it is hard to believe that a footballer can earn such money in one year. Maybe this is not true information, but I see that many different publications wrote about it today.
100% I am sure that Vincius rejected the offer, no matter how much the Saudi Arabian club spends to woo Vinicius it will not work. It seems that the Saudi Arabian club is overestimating a young player like Vinicius, a brilliant career in Europe, a candidate for the Ballon d'Or, Madrid proud striker and having a special place that can never be replaced in the main squad makes Vinicius a strong reason not to leave Europe too early. Moreover Vinicius is not a player who is hungry for money, his salary is more than enough in Madrid and all the club's existence. So don't expect him to go to the Saudi Arabian club.
I also think the same as you. It is impossible with Vini's good performance at Real Madrid he chose to move to Saudi Arabia, we know all players definitely want to play at Real Madrid, playing in the Saudi Arabian league his career will fade. Moreover, so far Vini has no problems with Real Madrid, Mbappe's presence will not shift Vini's position, it will actually make Real Madrid's front line even sharper.
In addition, Vini's enthusiasm to pursue individual records in the European arena is still very large plus being included in the strong candidates for the Ballon d'Or, of course this is the main reason that he will stay at Real Madrid. Actually, news like that is not true, it's just that sometimes the media likes to make controversial news to attract readers. Everyone knows, Vini is still very ambitious to win many trophies with Real Madrid.