I also think they can defend their championship in the French league, but when it comes to the Champions League, the probability may be lower. Because when you go to the eliminations outside of the group stage, every team can get surprising results. This year, the fight between Barcelona and Inter was the simplest example of this. While everyone expected Barcelona to win easily, Inter eliminated them. They made it to the final and played very badly against Paris Saint-Germain in the final. I don't know if Barcelona could have won the cup if they had made it to the final, but football is such a game, that's what I want to say.
Even if PSG wins the Champions League this season, it will be very difficult for PSG to retain this title next season. Some of the teams that we considered as favorites at the beginning of last season did not do well this season, but PSG won the Champions League title. Now, if Real Madrid, Manchester City and other strong teams return to the competition well next season, then it will be difficult for PSG to qualify for the semi-finals. I would like PSG to strengthen their team even more and recruit some important players to the club so that this French league team can compete well with Real Madrid and other teams if they perform well next season.
It is undoubtedly true that even if Paris Saint-Germain wins the UEFA Champions League this season, it will be much more difficult for PSG to retain this title next season. If they can buy and retain players in the same formation, it's safe to say they could have a chance next season but right now it doesn't look like they will recruit any players. The two teams you mentioned have already taken important steps, with Manchester City already signing four players, even we can say that Real Madrid Football Club has also been eyeing various young players, one of which is an Argentine player.