If we compare Real Madrid with PSG, maybe it is wrong because in terms of experience and quality, these two teams are different and Real Madrid has become the king of the Champions League. I am not so optimistic that PSG will be able to defend their second trophy in a row for next season because there are many challenges that they will get and also many teams are starting to fix their squads to look stronger when facing competition in the Champions League next season.
When PSG won the champions league in this previous season, nobody knew they would be the winners. And so we can't rule out that they can't do it in a row. Records are created when least expected, and as at those periods Real Madrid had to win the UCL back to back in a row little did any of us thought they could do it. PSG, right now has that quality and the experience provided that they have won the league, unlike before.
It is true that when PSG won the UEFA Champions League trophy in the just concluded UEFA Champions League competition, nobody knew they would be the winner because PSG was an underdog. But I don't see PSG winning the UEFA Champions League trophy next season because the UEFA Champions League competition is a difficult trophy to win back-to-back. PSG will only go far in the competition, but winning the UEFA Champions League trophy in 2 consecutive seasons isn't certain.