Interacting with files from sites like often involves modding your hardware. Always ensure you have a "Clean NAND" backup of your system before installing NSPs to avoid being banned from official Nintendo online services.
The file is a specific archive part for a Nintendo Switch game backup, likely Luigi's Mansion 3 . Handling multi-part archives and NSP (Nintendo Submission Package) files is a common task for enthusiasts of the Switch homebrew scene. Understanding Multi-Part Archives
An is a "Nintendo Submission Package". It is a format used for digital software on the Switch, containing the game ROM, icons, and metadata. These files are used by players to install digital backups or homebrew content onto a modified console. How to Use the Extracted File