The reason why Real Madrid lose against Juventus is Real Madrid use a strategy where it depend on Bellingham as an attacking midfielder. They're more comfortable when the midfielder backing up other midfielder and working together.
But it's clear there are so many chances in Real Madrid, but their strikers weren't able to maximize it.
This is a new debut for Jude Bellingham in Madrid, because it is still in a friendly match coach Carlo Ancelotti trying to find the right position for him, Ancelotti has made several game options throughout pre-season to find the maximum performance from all players. However, this defeat will see Ancelotti return to make more correcting in his first team before LaLiga starts
I think their problems are in defence, conceding 3-1 is proof of that. But it could be that the Madrid defenders are not playing to their full potential, because this is only a friendly match. Moreover the new season will start soon, avoiding the risk of injury is better and a priority. On the other hand, Ancelotti is reportedly a little worried about the results of Madrid successive defeats, after losing to Barca they lost again to Juventus.
If Ancelotti considers the results of pre-season matches important, then looking for a tough defender to wade through next season is a must, in the last four matches Madrid conceded eight goals. It would be useless to recruit Mbappe if their defense is weak.