How does "The Guest" by Albert Camus relate to existentialism?

While Camus himself did not identify as an existentialist, his works have had a significant impact on existentialism, and there are many elements of this philosophy to be found within "The Guest." In order to understand the importance of existentialism to this short story, it is necessary to dissect the major elements of existentialism and discuss how they present themselves throughout Camus's work.
Essential Nature
According to the tenets of existentialism, there is no essential nature in the world. This means that nature is entirely constructed of the choices each individual makes rather than the result of some inherent order in the universe. Another way to explain this concept is that nothing inherently has meaning other than the meaning and value the individual ascribes to it. Daru laments how little he and his unwanted guest matter to the harsh landscape of the desert, and yet neither of them would have any significant meaning outside of its barren context. While the prisoner seems to have the choice between freedom and imprisonment, fleeing would mean giving up all the meaning of the life he has created for himself.
Alienation
Both Daru and the prisoner are alienated from society by their own design. Alienation is a major theme throughout existentialism. Daru is alienated because he holds no allegiance to his country or to the society around him. The prisoner became alienated from society when he chose to commit a criminal act. Both men are alike in their alienation and the story's desolate setting reflects this.
Freedom
Freedom in existentialism is typically an illusory concept. The individual has the freedom to make his own decisions, but that comes with the burden of accepting the consequences of those decisions, which prevents him from being entirely free. The more freedom the individual obtains, the greater his isolation from society becomes. Daru illustrates this concept in his initial refusal to help the police. By refusing to take sides in the conflict between the French and the Arabs, he is cementing his own isolation from society. Existentialism leads to the realization that all restriction is self-imposed and, as the prisoner chooses to turn himself in at the end of the story, all individuals choose their own metaphorical prisons.
Choice and Consequence
Choice is a theme that runs throughout existentialism and the narrative of "The Guest," and it is related to all the other existentialist elements in the story. Daru makes an unusual choice to refuse to follow the orders of authority over his own morality, even though it will ultimately cost his life. Camus and the existentialists viewed morality as a construct of personal choice, and this decision marks the triumph of personal choice over obedience to authority. This choice comes with consequences, including Daru's almost inevitable execution at the hands of the Arabs who blame him for the prisoner's self-imposed isolation. This consequence can be seen as an existentialist metaphor for what can happen when rational choices are made in an irrational society.
https://plato.stanford.edu/entries/existentialism/