Real Madrid has often come from behind but they cannot afford to take it lightly this time as this is the first time the new format has been introduced, so if they don't take it seriously then they might just get knocked out. I agree that Ancelotti should have started thinking about benching Mbappe because besides being an option, it might make Mbappe better. There are times when a player can be better when he is left on the bench because he will reflect and try to improve himself to become a starter again.
When you say that, it's as if Mbappe has been the one making Real Madrid's game unusual and I don't think it's wise to make such an assessment. I don't think there's anything wrong with Mbappe, it's just that he still needs time to adapt.
Also remember the team's game as a whole, their problem is not just in the front line, but it's the whole thing. They have problems in defense and they still have problems in midfield, that's what makes Real Madrid's game messy so it's very difficult for them to get a win. So I disagree with what you said.
If Mbappe continues to perform below expectations, it is possible that Ancelotti will order him to sit on the bench. Now Mbappe feels quite a lot of pressure, Ancelotti has often defended him on many occasions by asking all parties to be patient and give him time. It must be admitted that it is not easy to become a main star at the Santiago Bernabeu, and Mbappe must work hard to prove his individual quality. Vinicius injury should be a momentum for Mbappe, because he can play in his ideal position on the left side. In addition, the storm of player injuries and the transition that has taken place within Real Madrid this season, collectively, of course, has also had an impact on Mbappe adaptation.