BTW - Sartre goes on later in life to claim that Marxism and Existentialism are basically identical, or rather that Marxism is the sociological analog to Existentialism in his work "Search for a Method". This is not very well known among anyone except the Sartre hacks, but is important to mention. Same with Camus and his early relationship with leftist politics.

Source if you don't believe me (see conclusion and checkout a full copy for further context): https://www.bard.edu/library/arendt/pdfs/Sartre-Search.pdf