Hey @ES_Avilon
Welcome to our community.
Make sure to close Steam properly and log back in with your account. Make also sure to have all your DLC packs enabled (click on the checkboxes in the game’s tab, DLC section). Then, right click on top of Conan Exiles and select Properties, Local Files, Repair. Let the process finish and download whatever it has to download. Once it’s done, try logging back into your single player game.