Im pretty sure that PSG will buy "star" players if they failed again this year (UCL).
PSG has offered a crazy contract 3 times bigger than Madrid bid to Mbappe, the club financial must be healthy.
This year might be not the year for PSG, but next year will be different.
For PSG aspect in the Champions League, I don't think they have any best season to win the Champions Leage more than last two seasons, but they failed, therefore, I don't think they will even go far this season. They have the chance of qualifying every season, but they couldn't win any one even though the team managements have tried so many coaches and players from different clubs.
Last season Real Madrid and Bayern Munich won most of their matches in the UEFA Champions League, and Bayern Munich even knocked out PSG, but when Bayern Munich and Real Madrid played Manchester City they couldn't perform well.
Playing match with Manchester City is not always easy because of the coach. Pep has various tactics that can be used to play different teams, and because of him being an experience manager, beating his team is always hard; that is why Bayern Mnich and Real Madrid find it difficult to bit them.