Distributing or downloading copyrighted Nintendo Switch games via NSP files is a violation of copyright law in virtually all countries. Nintendo actively litigates against ROM sites and has shut down emulators like Yuzu, citing piracy as the primary legal basis.
When dealing with game files for the Switch, you may encounter two main file formats: A dump of the actual physical cartridge. NSP: The digital, eShop version format. super smash bros ultimate nspbase gamepart