If there is a match against Real Madrid and the match is in Santiago Bernabeu, be assured that the referees will be on Real Madrid's side. Overall, it's a well-known fact that referees are biased in favor of the team that has match on their own stadium. It's also a well-known fact that referees are more forgiving to superstars and in some cases, to the teams of where these superstars play. For example, Messi is a superstar and every referee tries to avoid yellow or red card to him because if he gets benched, that will cause a huge protest in players since most of them come to watch his performance. When it comes to world cup, everyone wants Messi or Cristiano to win, so they treat Argentina and Portugal better but today it's not the thing to my mind since these two players are almost retired.
Maybe what you’re saying has a grain of truth. For example, when you watch the Champions League, it’s hard to deny that referees often seem to favor Real Madrid in certain controversial moments. Of course, this also happens in other matches, but since we watch games as fans, we naturally have a team we support, and if the referee makes a close decision in favor of the other team, it triggers negative emotions. But that doesn’t always mean the referee is biased toward one side or the other. Referees are human too, and they can make mistakes.