PSG's draw in Ligue 1 is unimportant, it does not affect anything, and as you said, it was not the main squad that played, that says it all.
Everyone knows that PSG want to win the Champions League, but this year PSG is acting very modestly without much publicity, about how important it is for them to win their first Champions League. Messi and Neymar left the team, without them no one hoped, that this would be possible. First rhem need to beat Barcelona, it seems to me that this is possible.
Whatever happens in Liga One cannot be used as a reference because the PSG team is very comfortable at the top of the standings so it doesn't affect anything when they get bad results.
And in the last match we could see that PSG rested many of its main players to watch the Champions League quarter-final match against Barcelona, this indicates that PSG really prioritizes the Champions League match.
PSG's target is to win the Champions League, even though this season their strength has decreased and they are not favored, but this team will certainly do their best in every Champions League match.
For the final match against Barcelona, I think it is still quite balanced and PSG still has the possibility of beating Barcelona because Barcelona's performance this season is also not that good.