It sounds like you're asking about a related to .wux files in The Legend of Zelda: Breath of the Wild (BotW), likely in the context of emulation (Cemu or similar).
. While the original WUD files for BotW are massive—typically 25GB regardless of the actual game data—the WUX format allows players to save significant storage space without losing game quality. What is a WUX File? botw wux file
file in its root directory containing the specific "Title Key" for the game and the Wii U "Common Key". Updates and DLC It sounds like you're asking about a related to