Editor script to automatically add scenes to Scenes in Build

ScenesInBuildConfigurator.cs

using System.Linq;
using UnityEditor;

namespace Foo
{
    [InitializeOnLoad]
    public static class ScenesInBuildConfigurator
    {
        private static string SceneName { get; } = "Bar";

        private static string SceneGUID { get; } = AssetDatabase
            .FindAssets($"t:Scene {SceneName}")
            .FirstOrDefault();

        static ScenesInBuildConfigurator()
        {
            if (ContainsScene())
            {
                return;
            }

            var scenes = EditorBuildSettings.scenes.ToList();
            scenes.Add(new EditorBuildSettingsScene(AssetDatabase.GUIDToAssetPath(SceneGUID), true));
            EditorBuildSettings.scenes = scenes.ToArray();
        }

        private static bool ContainsScene()
        {
            return EditorBuildSettings
                .scenes
                .Any(x => x.guid.ToString() == SceneGUID);
        }
    }
}