At Real Madrid, Alonso must first address the individual player issue. When Real Madrid's forwards get ahead, his passing is good, but when they get behind (as in yesterday's match against PSG), his passing weakens.
Mbappé takes the ball directly to goal and shoots. He doesn't even look to see if there's another player on his right or left. The same goes for Bellingham and Vini. All three of these players made the same mistake yesterday: They dribbled the ball all the way to goal and shot without even looking to see if there's another player.
Football is a team sport, and I believe Alonso's problem needs to be addressed.
PSG had a very high percentage of possession yesterday. They could have easily scored two or three more goals against Real Madrid.
Courtois played a key role in the 4-0 victory. He also made some impressive saves. Without these saves, the score would have been even higher.
To simplicity Madrid's problem is that based on the urgency.
1. Defense
2. Midfielder
3. Attackers.
I put their defense as the main proprity because of too many individual mistakes on their defenders. Many of their defenders are washed players. As for midfielder, performing a young, inexperienced, and lack of minutes midfielder to handle the game against PSG was bad decision, but give them a lot of experience.
Lastly, not much concern about their attack, but the same problem keep repeating, which is lack of team work.