key-retail.bin is a binary file that contains the necessary encryption keys for retail (commercial) Nintendo Switch games. These keys are required to decrypt and play games on a PC using the yuzu emulator.
Historically, Yuzu required a file named prod.keys (which contained text-based keys) alongside a title.keys file. As Yuzu evolved, the developers streamlined the process. In later builds (particularly EA - Early Access builds), the emulator consolidated these into a single binary file structure, often stored as key-retail.bin in the user directory. key-retail.bin yuzu
Here is the technical and legal reason: