One of the problems you mentioned was really visible at PSG apart from the perhaps less than harmonious relationship between the star players who were already in the PSG squad at that time. However, everyone also sees other things, such as the age of the star players who are no longer the same as before when they were at PSG and also the easy competition in Ligue1 for PSG to win the League every season. So that the players' skills and enthusiasm do not develop when playing in the Champions League.
PSG management has been trying to make their squad very perfect so far, even they did not hesitate to bring in Messi, Neymar and Donnarumma who were indeed the best players in the world at that time, when all the star players had gathered in the PSG squad of course there was no doubt if they could not get the Champions League trophy at that time, but what was seen was beyond all of our expectations when PSG was getting closer to the trophy they were actually Experiencing a defeat in the final match against Munich, PSG performance at that time was very good with Neymar and also Mbappe but unfortunately their mentality was still losing to Munich.
Currently I think the main problem of PSG is the cohesiveness of the team and also indeed the ligue 1 competition which has been classified as uncompetitive so far so that it does not test their mentality at all in playing in the champions league, although this season their squad is studded with stars but is not able to compete in the champion league of course we can compare it with Dortmund who only has a makeshift squad but is able to reach the final, So we can conclude that in addition to needing a qualified squad, of course, PSG must also have a strong mentality to compete in the Champions League and this they will never get as long as Ligue 1 is not competitive.