arch-8.x-1.x-dev/modules/checkout/modules/onepage/arch_onepage.routing.yml

arch_onepage.checkout:
  path: '/checkout/onepage'
  defaults:
    _title: 'Checkout'
    _title_context: arch_onepage
    _controller: '\Drupal\arch_onepage\Controller\OnepageController::checkout'
  requirements:
    _permission: 'access content'