While Fortnite is a game, downloading NSP files from unofficial third-party websites is generally discouraged for several reasons:

One of the most significant discoveries made by researchers is that seems to be linked to a specific version of the game, namely v17760256 . This version number suggests that the file may have been created or updated around a particular point in time, possibly corresponding to a significant update or patch.

The Switch version of Fortnite is a substantial download, often requiring between of space, depending on the current season's content. Epic Games How do I update Fortnite? - Epic Games