ref

using UnityEngine;

[ExecuteAlways, RequireComponent(typeof(ReflectionProbe))]
public class RealtimeReflection : MonoBehaviour
{
    public Transform target; // camera
    public Transform groundPlane;

    public ReflectionProbe probe;

    private Vector3 initialPosition;
    private Vector3 initialOffset;

    private void OnEnable()
    {
        probe = GetComponent<ReflectionProbe>();

        initialPosition = transform.position;
        initialOffset = probe.center;
    }

    private void OnDisable()
    {
        transform.position = initialPosition;
        probe.center = initialOffset;
    }

    // Update is called once per frame
    void Update()
    {
        if (!target || !groundPlane) return;

        var cameraHeight = Vector3.Dot(target.transform.position - groundPlane.position, groundPlane.up);
        var undergroudnPosition = target.transform.position - cameraHeight * 2 * groundPlane.up;

        probe.transform.position = undergroudnPosition;
        probe.center = initialPosition - undergroudnPosition;

        probe.RenderProbe();
    }
}