get_instance function

Autoloading removed the need of such method.
Now you have static service container which you can access to get DB or other service where you need it.
You can directly call objects which will be auto find.

Could you please share any documentations or example regarding this issue? What is the process to assess a LIBRARY within HELPER?

Thanks in advance.

If you examine a CIv4 helper source file you should find several examples. Here are a couple from url_helper.php

PHP Code:

$url = new \CodeIgniter\HTTP\URI($fullPath);
//or for a "service"
$config = \CodeIgniter\Config\Services::request()->config; 


In some cases, you might find it helpful to include a "use" directive in a helper. For instance, in form_helper.php you find

PHP Code:

use Config\Services; 


And then later in the file this simple piece of code uses "services"

PHP Code:

$request = Services::request();