Why is the object not written to the variable when searching by tag?

Question

C++ / C#

In my game, on the main stage, the canvas is called at startup. I tried to make it so that when switching to another scene and back, it was no longer active. I tried to do it with a tag, but for some reason the variable refuses to write the found object and always returns null. Although with Audio Sorce everything works fine.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class AlphaManager : MonoBehaviour
{
[SerializeField] private string SomeTag;
private void Awake()
{
GameObject canvasObj = GameObject.FindWithTag(SomeTag);
if (canvasObj != null)
{
Destroy(gameObject);
}
else
{
gameObject.tag = SomeTag;
}
}
}