Existential horror is a subgenre that deals with ideas of insignificance, isolation, and the unsettling fact that humanity is just a speck in a dark, uncaring universe; in short, it’s perfect horror movie fodder. Horror is filled with subgenres that are as basic as “slasher” to as specific and obscure as “screenlife”. There are just so many ways to pluck fear and terror out of the world, almost everything can be molded into something frightening. Existential horror is somewhere in the middle of well-known and vague, an unofficial grouping that includes some famous movies.

https://screenrant.com/existential-horror-subgenre-explained-examples/