This is the official format used by Nintendo for digital game files, DLCs, and updates found on the Nintendo eShop.
Mad Rat Dead is a stylized rhythm-platformer developed by and published by NIS America . Released in October 2020, the game follows a lab rat who is granted a second chance at life to seek revenge on the human scientist who experimented on him. MAD RAT DEAD ROM NSP UPDATE - Switch Game
This format is typically used for dumps of physical Nintendo Switch game cartridges. This is the official format used by Nintendo