EDIT:

I fixed this, using: the module_name.settings.yml file under module_name/config/install folder and also by using the module_name.module file where I've implemented the hook_form_alter() method.

So,

From my module_name.module file, here goes my code:

/**
 * Implements hook_form_alter().
 */

function modulename_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id){

    
     if($form_id === your_form_id){
        
        $form['#attached']['library'][] = 'module_name/route_name';
    // that's the route name you've defined in your module_name.libraries.yml file
    // where you've located the js file you're going to use

        $form['#attached']['drupalSettings']
        [module_name][route_name][send_this_variable_to_js] = \Drupal::config(module_name.settings)->get(key);

        return $form;
    }
    
    
}

Now in your JS file, you can console.log like this:

console.log(drupalSettings.module_name.route_name.server.send_this_variable_to_js)

Hope this help!