Real Madrid was terrible in that 4 - 0 loss, they couldn't even get the ball from PSG and if they managed to get it, less that 10 seconds they have handed it over to PSG. This was the case in the first half.
This is terrible, embarrassing, and disgusting.
If the core team had lost at least 4-3, that would still be perfectly reasonable and understandable, as long as they at least put up a fight. But here, 4-0, that's just nonsense.
As many members here have said, Xabi is responsible for this. He always uses speculative tactics, with his new tactics, placing several players in unusual positions, and being very efficient with the 4-3-1-2 formation.