It is difficult for PSG to win the title in the Champions League because the competition in the Champions League is more difficult than in the domestic league that PSG usually faces.
But PSG still has enough time to qualify for the next round of the Champions League so Luis Enrique has to try hard for this.
Indeed, PSG has quality players at their club, but it seems that Luis Enrique has not been able to develop a good strategy for PSG to be able to face competition in the Champions League because Luis Enrique does not have enough experience there, and it is possible that Luis Enrique will resign from coaching at PSG if Luis Enrique feel unable to make progress at PSG this season.
Yes, PSG has to let Mbappe go if Mbappe really doesn't want to extend his contract at PSG even though PSG will lose big because they don't make a big investment in Mbappe.
Mbappe also has a big dream of winning the UCL title and if at PSG it feels difficult for Mbappe to achieve it.
PSG must look for a coach who is experienced enough if they want to win the UCL title because they know that the squad that PSG has is quite good, it's just that they lack a mature strategy to can face UCL.
I don't think it's just PSG who will have difficulty winning the Champions League, even Man City, who is currently the defending champion, will find it difficult to defend it. Even Real Madrid, Bayern Munchen and other clubs will face the same thing, in the sense of facing their own challenges to realize their ambition of winning the UCL trophy, but PSG chances at this time are considered smaller than other favorite clubs. Looking at PSG condition, they should have the same opportunities as the others, because they have an even squad depth and an experienced coach. In fact, currently PSG is also having difficulties in Ligue 1, a competition that PSG has dominated for almost a decade.
I think Luis Enrique must first strengthen his foundations in Ligue 1 this season, to be consistent in every match. However, that doesn't mean their chances this season have disappeared in the UCL, what is clear is that they will need great luck if they win this season.