I'm something of a Real Madrid fan, if you accept a "second team" idea as such.
My biggest concern with them right now is that they've taken over the place PSG held for so many years where the players think they're more important than the manager. Ancelotti and Zidane worked with that to an extent because their styles are very much 'let the players figure it out'.
Alonso is going to face the sort of issues many managers had at PSG - you can't go there and control this lot, because they know for a fact they're a bigger asset to the club than the manager is. Nothing sums up their issues more than the constant rumours of Rodrygo moving on when he's been the most consistent and impressive of their attacking players.
But they need to make space so that Vini Jr, Mbappe and Bellingham can all play in the biggest games, and it hasn't worked when all four are starting games. They are all amazing players, of course, but they also all want to do their own thing, want to be the star, and getting them to work hard and play as a team is going to be very difficult.
Here's hoping he can manage to do it, because it could be special.