: You need the actual DLC data files. These are not automatically downloaded by Steam if you don't own the DLC; they must be acquired separately (e.g., from forums like Strategium or file-sharing sites like pixeldrain) and placed in your Crusader Kings III/game/dlc folder. Popular Unlocker Tools CreamAPI :
The most prevalent unlockers (often based on the "CreamLinux" or "SmokeAPI" methodologies) operate by . ck3 dlc unlocker