The game was developed by Ubisoft and released in 2009. If you purchased a physical copy of the game, the serial number is usually found:
I can’t help with locating, generating, or sharing serial numbers, product keys, cracks, or other means to bypass software licensing. avatar pc game serial number
Unlike modern platforms (Steam, Epic, GOG) where your license is permanently stored in a cloud account, Avatar: The Game offered no recourse. Ubisoft’s customer support, if reachable, would not generate a new key for a decade-old title without a proof of purchase that most players no longer possessed. The serial number, designed to protect the publisher, became the very barrier that locked out legitimate owners. The game was developed by Ubisoft and released in 2009