Everyone believes that Real Madrid will win the Champions League and La Liga because Mbappe is coming, but I am confident it will be difficult for any club to upset Real Madrid, but they will undoubtedly find a club that will face Madrid and win. Real Madrid has the most experience in the Champions League competition, with 15 UCL trophies.
Real Madrid is the most winners in UCL, it is not surprising if everyone favors Real Madrid as the candidate of UCL winner again for the next season. Moreover, Real Madrid can sign a top striker and a real machine goal, Mbappe. People will assume Real Madrid to be easier to win UCL next season because they have an additional power in attacking line. Even Real Madrid has no strong striker last season, they still could win UCL. With Mbappe, their chance to win UCL again this season should be higher.
Manchester City is the only club attempting to bring Real Madrid down and win the title. If not for penalty shootouts, Manchester City has the potential to defeat Madrid, Manchester City played well against Real Madrid, but Madrid's defense forced them to a penalty shootout. It will be interesting to see if Madrid can win back-to-back UCL titles under Ancelotti, who will undoubtedly do his best.
I think it is not only Man City that can defeat Real Madrid. In the few seasons ago, other teams also can defeat Real Madrid although it wasn't an easy match. Barcelona is one of the team that often defeated Real Madrid. Even if they are in bad financial condition, it is not impossible that they can defeat Real Madrid in UCL. Barcelona knows well Real Madrid, Real Madrid can't underestimate them although Real Madrid squad looks so strong.