PSG going well, they didn't play the parking bus scheme, PSG play as usual, Mbappe creates the first goal which indirectly creates high pressure on Barcelona team especially Lionel (failed penalty).
I think PSG didn't play as usual. In the second half, PSG played the defensive scheme, which we often see there are 10 PSG men in their defensive line, and sometimes they perform counterattacks when they had the opportunity (I think this is a reasonable strategy considering their opponents have 4 goals deficit).
So that Barcelona had more possession and tried to attack more, and occasionally can create some opportunities, but unfortunately, Barcelona had a poor finishing and looks hastily while in the PSG penalty area.