Barring his terrible defending for Liverpool's goal, if the intention of Pep is to use Cancelo as a wingback, which he basically does all the time on the left or right, then he has to play it with freedom.
Usually on the left, Cancelo can stay wide, come inside and switch with the winger, sit next to the holding midfielder to ping balls around, he likes freedom.
When you force him to stay wide, because you decided to play 4 midfielders rather than give him a true winger partner, you limit what he can do. He isn't a typical wingback who stays wide and just crosses in, he can do much more.
We already know he isn't a great defender, but don't limit the part of his game that is truly unique by making him a traditional wingback.