I think an important thing to also consider about "Crossroads of Destiny", which you touched on in your comment was about Zuko not being happy with his life in Ba Sing Se, and forcing himself to act happy for Iroh's sake - which is really no different than forcing himself to chase the Avatar regardless of personal cost for the sake of his father. They're both desperate attempts to gain approval, and Zuko's arc is so powerful because he ultimately discards that need for external validation.
I think there is a crucial difference between the two situations. Iroh never forces anything on Zuko. His main effort is trying to restore Zuko’s agency that Ozai took from him and give him a safe space to grow and figure out who he is and what he wants from life.
When Zuko chooses to free Appa, he’s finally ready to confront (in his fever dream) all his deepest demons and the lies he’s been telling himself, paralleling Aang’s meditation-journey through the chakras. So I think, the happy Zuko we see in Iroh’s teashop for a blessed day is not “faking” or forcing himself, but is a spiritually awakened version of Zuko who is able to look at the world in a fresh way and appreciate the simple blessings that came his way - a safe home, food on the table, his uncle’s love - instead of lamenting the things he’s lost.
But eventually, Zuko - just like Aang - was unable to fully open his seventh chakra and let go of his most prominent earthly attachment - his need for his father’s approval - leading to his choice to side with Azula.
But I agree that Zuko arc is so powerful, because he does get his “seventh chakra” moment not as a default of choosing to accept what he has because everything else is out of reach, but after getting everything he thought he wanted and he’s able to walk away from Ozai out of his own free will leaving all those attachments behind - country, family, wealth, power, romance.













