I still think Real Madrid is quite serious in building their team this season because their less than optimal performance lately does not mean that they should judge them as not serious in playing in every match. But it is more about the performance of their players who are a bit chaotic because there are old players who have retired and also there are new players who may not be used to the tactics in Real Madrid. So I will not judge them for seriousness or not because in reality they are really serious in every match even though the results may look different for this season.
More precisely because some of the players they have are injured so that Real Madrid's strength is much less consistent. They have lost twice in the Champions League so far and the defeats were against teams that were not too strong so there are many things that Ancelotti needs to fix and that is not talking about the draws they have gotten. Real Madrid remains the favorite in the Champions League because they do have a very good mentality in the league.
But if their strength is not much better and they do not play more solidly then I doubt they will be able to maintain consistency and it will be much more difficult to defend the title because currently there are many other teams that may have changed with much stronger and more solid strength.
A manager pre-sets the squad thinking that one or two players from the starting XI for the full time may be the maximum injury-prone players in their squad, and he places players on the bench. But something has been different for Real Madrid this season. Several players in the regular XI have been injured this season as well as the new striker not getting along well with the rest of the players but Real Madrid have failed so far. However, Real Madrid will not give up so easily, they will compete hard with the opposing teams with the players they have. They may have won the Champions League trophy last season but this season will be a tough journey for them but Real Madrid will still be among the favorite teams in the Champions League.