If you use the .wua (Wii U Archive) format or decrypted "Loadiine" folders (code, content, and meta), you generally do not need a keys.txt file. Keys are primarily required for: .WUD (Wii U Disc) files .WUX (Compressed Wii U Disc) files How to Obtain Cemu Keys
The Wii U, like modern consoles, encrypts all its software (games, updates, DLC) and system titles. Without the correct keys, the encrypted data is gibberish. Cemu needs these keys to: cemu keys