so newer games can run on older system versions. Merging updates and DLC into a single game file. Compressing files into NSZ format to save space. How to Obtain keys.txt
The keys.txt file contains the unique cryptographic keys used by the Nintendo Switch to secure its software. nsc builder keys.txt download
Note: This process requires a Nintendo Switch that is hackable (usually units produced before mid-2018) or a modded Switch. so newer games can run on older system versions