The two main types of Existentialism are Christian Existentialism, which integrates religious beliefs with existential ideas, and Atheistic Existentialism, which rejects the concept of a higher power or divine order in favor of individual freedom and responsibility.

Atheists have friends like anyone else; existentialism is irrelevant.

It does no such thing ! You may want to read about philosophy to learn what existentialism is.

Existentialism is a philosophical movement focused on individual experience and freedom of choice, emphasizing the importance of personal responsibility and creating one's own meaning in life. It addresses the fundamental question of human existence and the search for meaning in a seemingly indifferent universe. It suggests that meaning is not inherent in life, but rather constructed by individuals through their actions and decisions.

Existentialist epistemology is, like most existentialism, based on personal choice - i.e. a choice to believe.