Module development and code questions

I am trying to change core's routes with an event subscriber, but I am getting an error.

My code follows:

drupalup_route_alter.info.yml:

```

name: Drupal Up route subscriber
description: altering routes in our drupal instance
type: module
core_version_requirement: ^9

```

DrupalupRouteSubscriber.php:

```

<?php

namespace Drupal\drupalup_route_alter\Routing;

use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;

I have a custom module that originated in a D7 build, then migrated to D8, and now currently migrating to D9. Everything renders besides the iframe. When I look at the elements tab in the developer tools of chrome the div wrapper appears but there is no reference to an iframe. I get no errors in the console or in drupal reports. Does drupal not allow iframes to render from custom modules? the iframe code lives in the .module file, I've also tried rending it from the html.twig file and also tried rending a basic iframe from W3schools just to make sure my src was working.

Hi, 

I feel like I've done a lot of searching around and there's a lot of answers out there using hook_menu_alter, themes, overriding a service, but this is none of the above. The function that I'm trying to tweak is the execute function in views_bulk_edit contributed module in:

/src/Form/BulkEditFormTrait.php 

in a content type I have a select field linked to an entity reference
Through a callBack I update the select with the filtered values of the entity reference
The #option property is filled in like this

I am having an error, but I can't figure out why it occurs.

This is my event subscriber:

<?php

namespace Drupal\module_hero\EventSubscriber;

use Symfony\Component\EventSubscriber\EventSubscriberInterface;

use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Our events subscriber.
 */
class HeroInitSubscriber implements EventSubscriberInterface {

    public function __construct() {}

    public function onRequest($event) {    

    var_dump("Hello from our event"); die();
    } 

I've developed a Drupal 9 site in our "development" environment. I'd like to copy it to a "testing", "staging", and eventually a "production" environment. How do I do this without exporting/importing the entire database? I have many views, custom fields, content types, blocks, menus, and roles to export/import.

I use to be able to do this in Drupal 6/7. There were easy to use UIs to export/import views, blocks, and content types but not menus. Where are they now?