In the new Star Wars Movie The Rise of Skywalker, we can see Ray talking with Luke Skywalker on his island but his appearance is that of a ghost. As Luke Skywalker is a Jedi, did he really die, or did he become eternal after death? If so, why have all the other dead Jedi not become like him (Ex: Yoda)?
Luke is appearing as a Force Ghost.
The Force ghost was the soul and essence of a deceased Force-sensitive who denied the will of the Force upon death, yet was able to interact with the living. It also describes those who committed a final act of selflessness that led to their death, and have come to terms with it. Some Sith Lords learned similar techniques, which in some cases allowed them to physically interact with their environment.
Anakin, Yoda and Obi-Wan appeared as Force Ghosts at the end of Return of the Jedi.
The details of who can become a Force Ghost have changed over the course of the movies. Originally, it's just what Jedi did after death. Later, it became a lost technique, rediscovered by Qui-Gon Jinn, who taught it to Yoda and Obi-Wan after his death, and them teaching it to Anakin after his death. Presumably, one of them taught Luke to do the same.