Real Madrid's coach is managing the players well. If Vinicius and Mbapp get injured, then Arda will play a lot as a starter. Also, if Rodrygo gets injured, it opens up space for Arda to play more. The young player who is in the worst situation is not Arda, but Endrick, who has not even played at least 5 minutes in most games. Arda will have a place as a starter soon, but in Endrick's case, I doubt very much that he will have a place at Real Madrid. In my opinion, Endrick should accept being loaned to a Premier League team.
The many choices available will also make the coach have to really see who is ready to play, and of course they will have their own views about players who are really ready. Sometimes we feel too knowledgeable about players and even many of us question the players who are fielded in the match, while we don't really know the condition of the players themselves. I believe the coach has a strong reason why he plays a player and also doesn't play a player, yes, even though sometimes we are not satisfied with the results, but all decisions are in the hands of a coach.