That's how i figured out calculating my movement according to my camera's direction:

Note: There's TouchField because my game is for mobile. If yours not you need to calculate somethings different than mine.

void Movement()
{
    Vector2 vec = new Vector2(horizontal, vertical);
    vec = Vector2.ClampMagnitude(vec, 1f);

    Vector3 camF = cam.transform.forward;
    Vector3 camR = cam.transform.right;
    Vector3 rbVelocity = rb.velocity;

    camF.y = 0;
    camR.y = 0;
    rbVelocity.y = 0;
    camF = camF.normalized;
    camR = camR.normalized;

    targetPosition = (camF * vec.y + camR * vec.x) * MoveSpeed;

    Vector2 targetVelocity = (targetPosition - transform.position)/Time.deltaTime;

    rb.AddForce(targetPosition - rbVelocity, ForceMode.VelocityChange);

    transform.eulerAngles = new Vector3(transform.eulerAngles.x, transform.eulerAngles.y, Mathf.Clamp(transform.eulerAngles.z, 0, 0));

    Vector3 deltaPosition = transform.position - prevPosition;

    if (deltaPosition.sqrMagnitude > 0.1 * Time.deltaTime * Time.deltaTime)
    {
        transform.forward = deltaPosition;
    }

    prevPosition = transform.position;

    CameraAngle += FixedTouchField.TouchDist.x * CameraAngleSpeed;

    Camera.main.transform.rotation = Quaternion.LookRotation(transform.position + Vector3.up * 2f - Camera.main.transform.position, Vector3.up);

}

Here's how I calculated my movement according to my camera's direction:

Note: There's TouchField because my game is for mobile. If your game is not mobile you need to calculate somethings different than mine.

void Movement()
{
    Vector2 vec = new Vector2(horizontal, vertical);
    vec = Vector2.ClampMagnitude(vec, 1f);

    Vector3 camF = cam.transform.forward;
    Vector3 camR = cam.transform.right;
    Vector3 rbVelocity = rb.velocity;

    camF.y = 0;
    camR.y = 0;
    rbVelocity.y = 0;
    camF = camF.normalized;
    camR = camR.normalized;

    targetPosition = (camF * vec.y + camR * vec.x) * MoveSpeed;

    Vector2 targetVelocity = (targetPosition - transform.position)/Time.deltaTime;

    rb.AddForce(targetPosition - rbVelocity, ForceMode.VelocityChange);

    transform.eulerAngles = new Vector3(transform.eulerAngles.x, transform.eulerAngles.y, Mathf.Clamp(transform.eulerAngles.z, 0, 0));

    Vector3 deltaPosition = transform.position - prevPosition;

    if (deltaPosition.sqrMagnitude > 0.1 * Time.deltaTime * Time.deltaTime)
    {
        transform.forward = deltaPosition;
    }

    prevPosition = transform.position;

    CameraAngle += FixedTouchField.TouchDist.x * CameraAngleSpeed;

    Camera.main.transform.rotation = Quaternion.LookRotation(transform.position + Vector3.up * 2f - Camera.main.transform.position, Vector3.up);

}