Xabi Alonso is using a 4-player defense line for now unlike his preferences at Leverkusen. It was like that in his first two games in the FIFA Club World Cup at least. I think this is the best choice because they would have rotational problems for CBs otherwise.
In case of injuries I mean. Anyways, it was nice to see Arda Guler as a starter too. Xabi Alonso cares about him way higher than Ancelotti. Unlike him, he wants to have Arda adapted to midfield. To play in Modric's role maybe. Let's see whether it works...
It is not the case that the Real Madrid manager will adopt the same strategy in all matches. If he decides to use four defenders for all matches, the opponent will easily understand his strategy, which will make it easier for the opponent to plan their attack against them. In the first two matches that Real Madrid played in the Club World Cup, the opponents were relatively weaker than them and their main defender was not with their team, which is why he may have decided to play four defenders at the same time, but the strategy and defenders may change depending on the opponent. The strategy he used to manage the team at Leverkusen is the same strategy, but we have not seen him manage the team for Real Madrid, since he managed the team with a different strategy at Leverkusen, so it is clear from this that he has adopted such a strategy according to the needs of the team and he will not always adopt this same strategy.