Asset store assets are not allowed either, except for the ones that don't contribute to the game itself but make the workflow easier. You can use the tools that are in the Unity Package manager, except for the standard assets.

That says that your "don't contribute to the game itself" is for asset store things. But Package Manager things CAN contribute to the game itself (hence why it's a separate sentence). Cinemachine isn't an Asset Store asset anymore, it's a Packake Manager tool, so we can use it as much as we want