PSG's motivation will indeed continue to increase after successfully coming out as champions and maybe in the future they will try to maintain consistency in order to maintain the opportunity to defend the Champions League trophy. But if we talk about competition, maybe next season will be much more competitive so PSG themselves will certainly get much more difficult resistance. PSG can still be one of the strong clubs next season but I doubt their ability to defend the trophy because remembering the competition in the Champions League is not easy because there are many teams who may have evaluated the level of weaknesses that will be perfected.
PSG is a strong team but because this is the Champions League we certainly know that not many teams can defend the trophy in a row. This is a different competition from any other competition, maybe in Domestic PSG is used to doing it many times but in UCL I am not sure, because the title fight is not just about performance but many factors that each team must have. The first trophy is good enough to motivate PSG to stay focused but that does not mean they underestimate other teams who are preparing for the UCL next season.
PSG under Enrique is indeed unquestionable, PSG's game is increasingly collective and the attacks built are quite measured and effective, this can be proven after they managed to win the trophy they have always dreamed of this season. Next season their challenge will be even tougher, because as you said, defending the title is quite difficult, in the last decade, only Real Madrid has managed to win the title in a row, other clubs have not been able to. Lastly we remember when Man City in its best form was unable to defend the title, so looking at the history of other teams it is certainly difficult for PSG to defend the title.
However, in football anything can happen, the impossible can happen especially with the new UCL format like this season there are so many surprises that have occurred. In addition, PSG in the domestic league does not have significant pressure from other teams, this can be seen almost every season they always succeed in winning the title. So PSG will take this opportunity to stay focused on the champions league competition.