But what exactly is a WUX file? Why would you choose it over a standard Wii U Disc Image (WUD)? And most importantly, how do you get Breath of the Wild running smoothly using one?

to reclaim storage space while maintaining 100% compatibility. Integrity Verification

The WUX file format is a compressed version of the Wii U disc image format (WUD), specifically used by the Cemu emulator to play games like The Legend of Zelda: Breath of the Wild (BotW)