The answer comes down to .
If you wouldn't download the game ROM itself, you shouldn't download its key. The key is the lock; the ROM is the box. Both are protected intellectual property. Cemu Keys.txt
Cemu found a key for your title ID, but the key is incorrect—either corrupted, from a different region, or for a different game version (e.g., update vs. base game). The answer comes down to
The location of the file depends on your operating system and how you installed Cemu: but the key is incorrect—either corrupted