Script to attach an object to the HMD and update the pos/rot just before rendering

HeadAttach.cs

using UnityEngine;
using UnityEngine.InputSystem;

public class HeadAttach : MonoBehaviour
{
    public Transform Target;
    public InputAction HmdPosition;
    public InputAction HmdRotation;

    private void Awake()
    {
        HmdPosition.Enable();
        HmdRotation.Enable();
    }

    void OnEnable()
    {
        Application.onBeforeRender += ApplicationOnBeforeRender; 
    }

    private void OnDisable()
    {
        Application.onBeforeRender -= ApplicationOnBeforeRender; 
    }

    private void ApplicationOnBeforeRender()
    {
        Target.position = HmdPosition.ReadValue<Vector3>();
        Target.rotation = HmdRotation.ReadValue<Quaternion>();
    }
}