Enter Play Mode from the initial scene

EnterPlay.cs

using System.Linq;
using UnityEditor;
using UnityEngine;
using UnityEditor.SceneManagement;
using UnityEngine.SceneManagement;

[InitializeOnLoad]
static class EnterPlay
{
    private class SceneSetupObject : ScriptableObject
    {
        public SceneSetup[] sceneSetup;
    }

    private static readonly SceneSetupObject _sceneSetupObject;
    
    static EnterPlay()
    {
        _sceneSetupObject = Resources.FindObjectsOfTypeAll<SceneSetupObject>().FirstOrDefault();
        if (!_sceneSetupObject)
        {
            _sceneSetupObject = ScriptableObject.CreateInstance<SceneSetupObject>();
        }
        _sceneSetupObject.hideFlags = HideFlags.HideAndDontSave;
        
        EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
    }

    private static void OnPlayModeStateChanged(PlayModeStateChange stateChange)
    {
        switch (stateChange)
        {
            case PlayModeStateChange.ExitingEditMode:
                _sceneSetupObject.sceneSetup = EditorSceneManager.GetSceneManagerSetup();
                EditorSceneManager.OpenScene(SceneUtility.GetScenePathByBuildIndex(0));
                break;
            case PlayModeStateChange.EnteredEditMode:
                EditorSceneManager.RestoreSceneManagerSetup(_sceneSetupObject.sceneSetup);
                break;
        }
    }
}