You are likely using the official Ubisoft Connect or Steam version of the game. CODEX saves are for the cracked version. You will need to convert the CODEX save using ACSaveTool to work with your official version. Alternatively, locate your official save path (e.g., ...\Ubisoft Game Launcher\savegames\<user-id>\4923 ), but remember, manual replacement will be more complex due to encryption.
From the results for "Assassin's Creed Origins save file location PC", result 4 (pcgamingwiki.com) is a reliable source. I'll open it. --- Assassin 39-s Creed Origins Save Game Level 30 Codex
If the game does not recognize the save, ensure the file name matches the expected slot (e.g., You are likely using the official Ubisoft Connect
If this folder path does not exist, you may need to launch the game at least once. The game will automatically generate the correct folder structure during its first startup, which is often necessary to ensure your save file is placed correctly. Alternatively, locate your official save path (e