ds-8.x-3.9/modules/ds_extras/ds_extras.routing.yml

ds_extras.switch_view_mode:
  path: '/ds-switch-view-mode/{entityType}/{entityId}/{viewMode}'
  defaults:
    _controller: '\Drupal\ds_extras\Controller\DsExtrasController::switchViewMode'
  requirements:
    _permission: 'access content'
    _custom_access: '\Drupal\ds_extras\Controller\DsExtrasController::accessSwitchViewMode'