The first thing to check if you are in this situation is whether your system is using a processor that supports the AVX instruction set. To use the in-game video recording tool, your processor requires this instruction set. Please check the system requirements for more information.
If your processor supports AVX, please verify your game's files (Steam, Ubisoft Connect) and try again.
Should the problem persist, feel free to contact our support teams! In technical cases such as this, our agents require a Dxdiag and MSinfo file to investigate. You can speed up the process by attaching both files when you create your ticket. Thank you!