I see many people saying that TLJ deconstructs the myth of Star Wars. I think this is a valid interpretation, but not entirely true. In my view this movie tests the myth, yes, it creates terrible (and incredible) obstacles for the heroes, making them question what was once unquestionable. “dead heroes”, as Leia told Poe, reminding us that in fact not everything serves a divine purpose as we usually believe for these films.
But after the dark journey that was the TLJ, we have a much more powerful myth, in my opinion. One that goes beyond the old norm, because it does not abandon what has already been, it just puts to the test and adds the new concepts. Luke in Crait was real, he inspired the Galaxy, saved the resistance and faced his biggest mistake, Ben. He was a great hero, but still only a man capable of making mistakes.
All the characters in this movie have their truths tested and evolve from that. Just as the film itself tests the truths of the saga (as TESB and TPM did before). I agree that this film has a postmodern side, consequent of the time in which we live, but I do not think that it left the myth, only magnified.
I hope I have been clear, I will also leave some very good videos that I found about Star Wars as a whole. The first (in two parts) talks about the myth of the saga, the interesting thing is that the person in the video had not watched TLJ yet and his predictions turned out to be quite accurate. The second is another social analysis of the character Anakin and the Jedi order, worth seeing.