An NSP file is a digital package format used by the Nintendo Switch for games and updates. When you see this file wrapped in a .rar archive on third-party websites, you are looking at content that has been stripped of its digital rights management (DRM).

Nintendo Switch 2 Edition

Since this 1.1.1 release, several more substantial updates have been released, particularly for the of the game:

Part 1: What is "Super-Mario-Party-Jamboree-Update-1.1.1.NSP.rar"?

you can unlock in this version or details about the more recent Version 2.0.0 How to Update Super Mario Party Jamboree | Nintendo Switch

The file Super-Mario-Party-Jamboree-Update-1.1.1.NSP.rar is a compressed archive containing:

File Size:

The 1.1.1 NSP update is approximately 1.2 GB. When compressed into the RAR format, it reduces to roughly 980 MB.