PSG's performance at the start of this season did indeed decline slightly compared to last season, but slowly they can continue to develop their team's performance in a more positive direction and that makes their chances in the last 16 of the UCL even greater and the opponent they face is Real Sociedad, if We look at the quality of both teams. I think PSG is a little better than Real Sociedad, so I don't doubt that PSG's percentage of getting to the next round is much greater than Real Sociedad.
With respect to their domestic league, PSG did started on a relatively poor note but later were getting back to form and quickly got to the top of the table this season and now they are more likely to be the winners of the Ligue 1 as they are like the most formidable team in the Ligue 1 currently, their team form and Dept looks better than others.
Due to their dominance in their local league, I think they are showing some lax and negligence to the league but back in the UCL they are doing much better as they were able to get pass the group stage although with much struggle so they are gradually getting through the UCL even with their struggles, playing against Real socidad is going to be a struggle because real sociadad is doing well and they are also not weak both on the UCL and their local league so it's very possible it's ends in a draw in the first leg.
PSG has been able to recover quite well so far, I think they are not going to have any problem trying to be the winner of Ligue 1. But if we are talking about the UCL they definitely are going to have a lot of problems. Because in UCL they are facing a lot of teams that are actually better than them and they actually have competition in the UCL. That is a big reason I don't think that they will win the UCL. You can not prepare for the biggest competition of football by playing against some mid-teams throughout the whole season. And yes I do not think they will be able to win the UCL this season as well. They are just not good enough.