HideSceneViewToolbar.s

using UnityEditor;
using UnityEngine;
using UnityEngine.UIElements;

public class HideSceneToolbar
{
    [MenuItem("Test/Hide the scene toolbar")]
    static void Hide()
    {
        var sceneViews = Resources.FindObjectsOfTypeAll<SceneView>();
        foreach(var sv in sceneViews)
        {
            var toolbar = new VisualElement();
            toolbar.style.backgroundColor = new Color(0.2196079f, 0.2196079f, 0.2196079f);
            toolbar.style.height = 20;
            toolbar.BringToFront();
            sv.rootVisualElement.Clear();
            sv.rootVisualElement.Insert(0, toolbar);
        }
    }
}