futtern/config/routes/framework.php

<?php declare(strict_types=1);

use Symfony\Component\Routing\Loader\Configurator\RoutingConfigurator;

return static function (RoutingConfigurator $routingConfigurator): void {
    if ($routingConfigurator->env() === 'dev') {
        $routingConfigurator->import('@FrameworkBundle/Resources/config/routing/errors.xml')
            ->prefix('/_error');
    }
};