In my opinion, the reason Real Madrid gave the number 10 to Mbappe was probably to signal that he is now the one holding the "torch" at Real Madrid, after the number was vacated by Luka Modrić. The number signifies hope, responsibility, and the potential to create miracles on the field, especially considering Real Madrid's poor performance last season, it is hoped that Mbappe can be more motivated to improve Real Madrid's performance. and I feel that Mbappe will not take this lightly, there will definitely be more responsibility that he will shoulder, and it is not an easy matter.
Yes, that's right. Jersey numbers in football are indeed very sacred because certain numbers carry the highest expectations for each team. However, if I'm not mistaken, when Arda arrived at Real Madrid, he was even touted as Modric's replacement, and many people thought the number 10 would be given to Arda. I also think Arda wanted the number 10, but the club decided to keep it for Mbappé.
Furthermore, if we look at Real Madrid's jersey numbers, players who typically wear the number 10 are often identified as midfielders. Mbappé is more suited to the number 9 or 7, as he's a forward, but now it's his and the club's choice. Hopefully, he can bring hope and glory to the team, as you mentioned.
The consideration may be that Arda has not yet reached the same level of quality as Mbappe, whose achievements we all know well. Mbappe is more experienced, has already won a World Cup, and is one of the best players in the world, which makes him more deserving of the number 10 jersey compared to Arda. Even though Mbappe is more suited to playing as a forward, Xabi likely sees the potential for him to also become a “playmaker” in the Real Madrid team, and I am also confident that he is capable of carrying out the duties of that position.