Add a template path to any location, includes plugins/modules as well as the native templates directory

Helpers.php

<?php

namespace yellostudio\helpers;

use Craft;
use craft\base\Plugin;
use yii\base\Event;
use craft\web\View;
use craft\events\RegisterTemplateRootsEvent;

class Helpers extends Plugin {

  public static Helpers $plugin;

  public function init(): void 
  {

    parent::init();
    
    self::$plugin = $this;

    Craft::setAlias('@helpers', $this->getBasePath());

    if ( getenv('CRAFT_ENVIRONMENT') == 'dev' ) {
      Event::on(View::class, View::EVENT_REGISTER_SITE_TEMPLATE_ROOTS, function (RegisterTemplateRootsEvent $event) {
        $event->roots['helpers'] = Craft::getAlias('@helpers/templates');
      });
    }

  }

}

{{ include('helpers/foo') }}

Will now look for a foo.twig file in /vendor/yellostudio/helpers/src/templates/foo.twig. If the file doesn't exist, it will then fallback to the standard /templates/helpers/foo.twig file.

This prevents the need to do something like this:

$oldMode = \Craft::$app->view->getTemplateMode();
Craft::$app->view->setTemplateMode(View::TEMPLATE_MODE_CP);
$html = \Craft::$app->view->renderTemplate('plugin-handle/path/to/template');
Craft::$app->view->setTemplateMode($oldMode);