How to define frontend theme (non-admin) for a given node tab route?
The _node_operation_route option respect the Use the administration theme when editing or creating content, if you want to explicitly disable admin theme for this node-related page don't use _node_operation_route

The _node_operation_route option overrides _admin_route https://api.drupal.org/api/drupal/core%21modules%21node%21src%21EventSubscriber%21NodeAdminRouteSubscriber.php/function/NodeAdminRouteSubscriber%3A%3AalterRoutes/8.8.x