In Expressive, we have standardized on a file named config/routes.php to contain all your route registrations. A typical file might look something like this:

declare(strict_types=1);

use Zend\Expressive\Csrf\CsrfMiddleware;
use Zend\Expressive\Session\SessionMiddleware;

return function (
    \Zend\Expressive\Application $app,
    \Zend\Expressive\MiddlewareFactory $factory,
    \Psr\Container\ContainerInterface $container
) : void {
    $app->get('/', App\HomePageHandler::class, 'home');

    $app->get('/contact', [
        SessionMiddleware::class,
        CsrfMiddleware::class,
        App\Contact\ContactPageHandler::class
    ], 'contact');
    $app->post('/contact', [
        SessionMiddleware::class,
        CsrfMiddleware::class,
        App\Contact\ProcessContactRequestHandler::class
    ]);
    $app->get(
        '/contact/thank-you',
        App\Contact\ThankYouHandler::class,
        'contact.done'
    );

    $app->get(
        '/blog[/]',
        App\Blog\Handler\LandingPageHandler::class,
        'blog'
    );
    $app->get('/blog/{id:[^/]+\.html', [
        SessionMiddleware::class,
        CsrfMiddleware::class,
        App\Blog\Handler\BlogPostHandler::class,
    ], 'blog.post');
    $app->post('/blog/comment/{id:[^/]+\.html', [
        SessionMiddleware::class,
        CsrfMiddleware::class,
        App\Blog\Handler\ProcessBlogCommentHandler::class,
    ], 'blog.comment');
}

and so on.

These files can get really long, and organizing them becomes imperative.