Rotate a vector in unity

On paper, it seems like a simple issue, but ive been stuck on it all day. The issue is that there are many ways that I cant rotate this because i have additional things that i am going to add later that wouldnt work for many of these solutions. I am making a 3rd person player controller (top down perspective like foxhole or wasteland 3).

The issue i have is that the player needs to move relative to the camera, but rotate independently of it. Pressing A and D will move the character left and right relative to the camera, W and S forward and back relative to camera. However, I need to be able to have the character rotate independently of the camera, so i need to be able to face any direction while still moving the character relative to the camera as the rules above tell it to.

        Vector2 targetHorizontalMoveDirection = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
        Vector2 horizontalMoveDirection = Vector2.MoveTowards(horizontalMoveDirection, targetHorizontalMoveDirection.normalized * maxSpeed, movementAcceleration*Time.deltaTime);
        Vector3 finalMoveDirection = new Vector3(horizontalMoveDirection.x, 0, horizontalMoveDirection.y);

        if(finalMoveDirection != Vector3.zero)
        {
            playerCharacterController.Move(finalMoveDirection * Time.deltaTime);
        }

I would like to keep the first 3 lines mostly as they are, as that gives the movement weight and acceleration which id like to keep. I feel an ideal solution would be something between finalMoveDirection and Controller.move that lets me rotate the finalMoveDirection Vector to get a new vector that has a forward direction that matches the direction the camera is facing.

One solution that i tried but couldnt quite figure out was something like this, the only thing i really changed was the character controller line.

playerCharacterController.Move(
(finalMoveDirection.x*cam.transform.right)+
(finalMoveDirection.z*cam.transform.forward)+
(0f*Vector3.up)
)

This sort of worked but the issue was that the camera is angled down and points into the floor, meaning trying to walk forwards and back would cause you to walk towards the camera, into the air, or forward, into the ground. If theres a way to get the forward direction of the camera without having it point into the ground (like if it was looking completely straight) then that could work also, but i couldnt figure that out. I feel like this could be a likely solution but if i could rotate the vector to be level to the ground, what would be stopping me from just rotating the move vector to just face away from the camera in the first place?

Theres a number of other solutions i tried, like using Mathf.Atan2 to get an angle and then using Quaternion.AngleAxis to rotate the vector, which didnt work. I tried a bunch of stuff that i cant remember now but so far no luck.

As per usual, i figure it out the moment i ask the question. I still feel like it should be answered though in case anyone else needs it.

        Vector2 targetHorizontalMoveDirection = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
        Vector2 horizontalMoveDirection = Vector2.MoveTowards(horizontalMoveDirection, targetHorizontalMoveDirection.normalized * maxSpeed, movementAcceleration*Time.deltaTime);
        Vector3 finalMoveDirection = new Vector3(horizontalMoveDirection.x, 0, horizontalMoveDirection.y);

        if(finalMoveDirection != Vector3.zero)
        {
            Vector3 CameraVectorParallelToGround = Vector3.ProjectOnPlane(cam.forward, Vector3.up);
            playerCharacterController.Move(
                (
                (finalMoveDirection.x * CameraVectorParallelToGround.normalized) +
                (Vector3.up*0f)+
                (finalMoveDirection.z * CameraVectorParallelToGround.normalized)
                )
                * Time.deltaTime);
        }

'cam' is the transform of the camera. And 'playerCharacterController' is the character controller component on the player.