With the many UCL trophies that Real Madrid has won, in my opinion it is the best European team in history, and there are still other best teams, but Real Madrid is the highest caste team, whoever the team that faces it will definitely feel afraid, as will its arch enemy in Laliga, namely Barcelona, which is more often meets with Real Madrid. Yes, even though there are several teams that can beat Real Madrid, whether in the UCL or Laliga, Real Madrid's performance in a competition as big as the UCL will still be more focused on achieving it, so it's only natural that in the UCL, Madrid is always the team they fear.
Real Madrid is the king of the UCL, they are the team that has the most UCL titles and they are the only team that has won the UCL three times in a row, thus the mentality and self-confidence of the Real Madrid team is better than other teams so that is what makes they are very much appreciated.
The quarter-final match against Manchester City will indeed be very difficult for Real Madrid, but they will also be very focused on this match because in the domestic league the Real Madrid team is currently quite comfortable at the top of the standings without any pressure from their rivals.