Luke Skywalker has returned... AND Luke Skywalker has vanished.
Yes, Luke returned, but he returned to Tattoine and although he was referenced as Jedi Knight, he was not yet a Jedi. As even Bib Fortuna discovers:
Even u/ugnaught77 clarifies for another Redditor:
He didn't become a Jedi until he confronted Vader. Then, only then, a Jedi was he.
This was followed up by u/quarryfresh, who described how the Jedi's return was not in reference to Luke, but Anakin.
I was discussing this the other night with some friends and I realized, Luke is not the Jedi referenced. He was unable to complete his training and never killed Vader as Obi Wan pushed him to do. The Jedi returning is Anakin, as he rejects the Dark side and moves to the Light in those glorious seconds to kill Darth Sidious as he should have long ago.
Another Redditor responded saying, he was wrong. So. u/quarryfresh followed up with quotes from the Return of the Jedi that seem to show he was indeed correct, Anakin is the Jedi returned.
Yoda: No more training do you require. Already know you, that which you need.
Luke: Then I am a Jedi.
Yoda: No. Not yet. One thing remains. Vader. You must confront Vader. Then, only then, a Jedi will you be. And confront him you will.
When Yoda dies, he tells Luke he is not yet a Jedi. This is after others (and even himself) has referred to him as a Jedi or Jedi Knight variously. Here we find that those references were premature, at least Yoda's eyes. Moments later, Obi-Wan Kenobi appears as a Force Ghost and tells Luke the truth about Anakin becoming Darth Vader. He tells Luke that he must kill Vader.
Obi-Wan: You cannot escape your destiny. You must face Darth Vader again.
Luke: I can't kill my own father.
Obi-Wan: Then the Emperor has already won. You were our only hope.
Luke tells Obi-Wan, "There is still good in him." He believes his father, Anakin, the Jedi Master, is still inside Darth Vader and can be returned. The next time he sees Vader he probes him for any vestige of Anakin.
Darth Vader contends that he is all Dark side now, but Luke still tries to tell him that he knows there is good in him. He knows Anakin is in there somewhere and will return. Luke gets his wish when Vader sacrifices himself to save his son, redeeming himself as Anakin, Jedi and father of Luke.
Once his helmet is removed, Vader is gone and we see that Anakin has returned.
Luke: No. You're coming with me. I'll not leave you here, I've got to save you.
Anakin: You already... have, Luke. You were right. You were right about me. Tell your sister... you were right.
Redditor u/quarryfresh writes:
What was Luke right about? There was good in Vader returning. Anakin was still in there and he has returned. The Jedi has returned.
The Jedi has indeed returned and that Jedi is Anakin, not Luke.