Reverse engineering software (and even using small bits of proprietary code when required) in order to make it compatible with other hardware is fully legal (tons of precedent, for emulation specifically see Sega v Accolade and Sony v Connectix), and selling emulators commercially is also fully legal (Sega v Connectix was about a commercial Playstation emulator for the Mac, Sony v Bleem was about a commercial emulator for the PC and Dreamcast)

Nintendo’s legal claims against Yuzu are completely untested and dubious at best, it’s the threat of spending millions of dollars on lawyers that’s very real and effective, they are yet again simply weaponizing the courts and the DMCA like all the other corpo scum before them