Add open/active scene to the build settings as last scene or (!!!) second to last scene using menu item or shortcuts.

AddSceneToBuildSettingsShortcut.cs

using UnityEditor;
using UnityEngine;
using UnityEditor.SceneManagement;

// inspired by https://answers.unity.com/questions/205742/adding-scene-to-build.html?_ga=2.184209894.1575122923.1603913761-831749454.1600446627

public static class AddSceneToBuildSettingsShortcut
{
    [MenuItem("Game/Add scene as last build scene &a")]
    private static void AddAsLastBuildScene()
    {
        EditorBuildSettingsScene[] original = EditorBuildSettings.scenes; 
        EditorBuildSettingsScene[] newSettings = new EditorBuildSettingsScene[original.Length + 1]; 
        System.Array.Copy(original, newSettings, original.Length);
        EditorBuildSettingsScene sceneToAdd = new EditorBuildSettingsScene(EditorSceneManager.GetActiveScene().path, true); 
        newSettings[newSettings.Length - 1] = sceneToAdd;
        EditorBuildSettings.scenes = newSettings;
        Debug.Log("Added scene " + EditorSceneManager.GetActiveScene().name + " as the last scene in build settings");
    }

    [MenuItem("Game/Add scene as second to last build scene #&a")]
    private static void AddAsSecondToLastBuildScene()
    {
        EditorBuildSettingsScene[] original = EditorBuildSettings.scenes; 
        EditorBuildSettingsScene[] newSettings = new EditorBuildSettingsScene[original.Length + 1]; 
        System.Array.Copy(original, newSettings, original.Length);
        EditorBuildSettingsScene sceneToAdd = new EditorBuildSettingsScene(EditorSceneManager.GetActiveScene().path, true);
        newSettings[newSettings.Length - 1] = newSettings[newSettings.Length - 2]; // swapping the scenes
        newSettings[newSettings.Length - 2] = sceneToAdd;
        EditorBuildSettings.scenes = newSettings;
        Debug.Log("Added scene " + EditorSceneManager.GetActiveScene().name + " as second to last scene in build settings");
    }
}