This is their biggest trophy ever. But i think this season they werent confident in winning the champions league. The owner himself said that they didnt expect to win it this year but yet they did. I dont know if anyone remembers but PSG barely passed the league phase in the champions league and managed to win the title and this adds a lot to their achievement this season
Seeing that they were unable to win the trophy when they had some of the best players, it is not out of place to assume that they wouldn't win the UCL. The club even lost their main player Kylian Mbappe to Real Madrid, which complicated their challenge. Nasser Al-Khelaïfi has achieved his long-time desire to win this prestigious trophy. A club that had to go through the playoff to qualify for the second round didn't really look like a team that would win the competition. So I am not surprised that the owner of the club didn't expect them to win the UCL this season.