Meet Traversable Menu Module!
When we have a very complex multilevel menu and we need to make it extremely user-friendly the Traversable Menu approach could be the option.
I knew the JS library by Jim Keller (https://github.com/jimkeller/traversable_menu) that can provide such functionality out-of-the-box. I just had to wrap it into a Drupal module.
Now the module was released with the minimum number of settings. Please visit its page https://www.drupal.org/project/traversable_menu.
Of course, the library provides better flexibility. But additional options will be done soon. Now I just would like to get feedback from the community.
The installation and the setup process is very easy:
1. Download the module or install it with composer ("$ composer require drupal/traversable_menu").
2. On the admin page "/admin/structure/block" place a new block in the region that you want to have the menu.
3. Select the menu that you are going to use as the Traversabel one.
On the first animated image in the post, you can see how the native admin menu can work as the Traversable one.