How can I add a trailing slash to TYPO3 v9 URLs?

To always add an appending /, you can create yourself a route enhancer decorator and put it in your site package.

Create a file in your site package under Classes/Routing/Enhancer/ForceAppendingSlashDecorator.php with the content:

<?php
declare(strict_types=1);
namespace MyVendor\SitePackage\Routing\Enhancer;

use TYPO3\CMS\Core\Routing\Enhancer\AbstractEnhancer;
use TYPO3\CMS\Core\Routing\Enhancer\DecoratingEnhancerInterface;
use TYPO3\CMS\Core\Routing\RouteCollection;

class ForceAppendingSlashDecorator extends AbstractEnhancer implements DecoratingEnhancerInterface
{
    /**
     * {@inheritdoc}
     */
    public function getRoutePathRedecorationPattern(): string
    {
        return '\/$';
    }

    /**
     * {@inheritdoc}
     */
    public function decorateForMatching(RouteCollection $collection, string $routePath): void
    {
        foreach ($collection->all() as $route) {
            $route->setOption('_decoratedRoutePath', '/' . trim($routePath, '/'));
        }
    }

    /**
     * {@inheritdoc}
     */
    public function decorateForGeneration(RouteCollection $collection, array $parameters): void
    {
        foreach ($collection->all() as $routeName => $existingRoute) {
            $existingRoutePath = rtrim($existingRoute->getPath(), '/');
            $existingRoute->setPath($existingRoutePath . '/');
        }
    }
}

Please replace set the correct namespace matching your site package.

To register your route enhancer, add the line to your ext_localconf.php:

$GLOBALS['TYPO3_CONF_VARS']['SYS']['routing']['enhancers']['ForceAppendingSlash'] = \MyVendor\SitePackage\Routing\Enhancer\ForceAppendingSlashDecorator::class;

As a last step, put the following code into your site configuration yaml file:

routeEnhancers:
  PageTypeSuffix:
    type: ForceAppendingSlash

After this adjustments, TYPO3 will always add an appending / to your URLs so the new URLs will match the old ones created by realurl.

You can use the PageTypeEnhancer for mapping &type parameter in your site configuration (config.yaml file):

routeEnhancers:
  PageTypeSuffix:
    type: PageType
    default: '/'
    index: ''
    map:
      '/': 0