Can't just explain what went wrong with Les Parisiens but it seems that the players are not fit or suffering from fatigue. They were relatively outsmarted and bulldozed by the Newcastle player. I know Mbappe can't wait to leave this club because he needs to chase his dreams somewhere else.
PSG is lack of good players, there are still many mediocre players in their club. Take a look with Newcastle where they don't have any super stars, but all their players are in good quality.
I disagree for Mbappe can't wait to leave PSG, if he want to leave PSG, he wouldn't renew his contract until 2026.
PSG will not able to win Champions League as long as they only focus to sign star players.
PSG do not lack good players, rather they most likely lack good tactics enough to have won that game,the problem with PSG is never good players as last summer window they did signed good players and it was more like every of they positions were in check, from the defence up to the forward/attacking line. It's most likely they needed a good tactics that will position the players rightly.
Nevertheless Newcastle isn't a small or weak team either, they have been really good and started the season on a very brilliant not in the EPL so they wouldn't be considered an easy one for PSG, Newcastle aswell had the home advantage over the visiting french side, most English teams except for Manchester united, have been performing really well in the UCL this week.
Definitely mbappe is not staying in PSG any season longer as they are no longer fit for his career, I think PSG is gradually becoming a mediocre team and it's no longer healthy for his talent, most likely by the end of this season he should be leaving although there are speculations his contract is till 2025 but I doubt how authentic that information is because there is yet an official Statement to confirm it.