I’ve seen this question before…I think this is the answer (copy & paste from the tech docs)
“Landscapes are divided into multiple Components, which are Unreal’s base unit of rendering, visibility calculation, and collision. Components in a Landscape are all the same size and are always square. The size of the Landscape component is decided when the Landscape is created and the choice depends on the size and detail of the Landscape you wish to create.” From: Landscape Technical Guide | Unreal Engine Documentation