How do I load a view from outside the default views folder in this application?

I am working on a CMS with [b]CodeIgniter 3.1.8[/b] and Bootstrap 4. I have decided to add themes to it.

The [i]themes[/i] directory is outside [i]application[/i] as can be see in the image below:
[color=var(--blue-700)]
Inside [i]themes[/i] I have the theme directory (of course) which contains the "master view",  layout.php:
[/color][color=var(--blue-700)]
In application/core [/color]I have added a Loader.php file with the following contents:

Code:

<?php defined('BASEPATH') OR exit('No direct script access allowed');
require APPPATH."../system/core/Loader.php";

    class MY_Loader extends CI_Loader {
   
      function ext_view($folder, $view, $vars = array(), $return = FALSE) {
        $this->_ci_view_paths = array_merge($this->_ci_view_paths, array(APPPATH . $folder . '/' => TRUE));
        return $this->_ci_load(array(
                '_ci_view' => $view,
                '_ci_vars' => $this->_ci_prepare_view_vars($vars),
                '_ci_return' => $return
            ));
      }
   
}?>

In my Posts controller's index() method, I load the view passing it the data:

Code:

public function index() {
    //more code here
     $this->load->ext_view('third_party', 'themes/caminar/layout', $data);
}

I get this error message:

Code:

Call to undefined method CI_Loader::ext_view()

[b]NOTE:[/b] the application is [b]not HMVC[/b], only MVC.

What am I doing wrong?