Indeed, it will not be easy for a club to maintain their UCL title in a row, besides the three clubs you have explained, there is also Barcelona who still has the spirit to be much stronger, Napoli with their return to the top position of Serie A, and Bayern Munich, and maybe Man City (although doubtful when looking at their performance in the Club World Cup).
So far, only Real Madrid has been able to defend the UCL title more than 2 times, PSG was very lucky to win the first UCL trophy since being taken over by Nasser Al-Khelaifi, this success marked the starting point for them to return to glory in European competition. Challenges from several top European clubs make it difficult for PSG to defend the trophy they have just won, but they also have the quality to continue to dominate (as long as they can maintain their best performance).

Barcelona have improved dramatically under Hansi Flick, Liverpool and Bayern Munich are also always strong contenders. Real Madrid, who have just formed a new force after the end of the Ancelotti era, have also begun to show their depth in the Club World Cup. Regarding Man City, I also still have doubts about their abilities (based on their recent performance).