Drupal 8.x

I'm starting to migrate from drupal 7 to 8 modules, I've google for several hours now, but why does this code  not work?,  i get 'This browser does not support HTML5'. If i put the video html part in a html file in the root the video  or in a drupal 7 module it will appear.

<?php

namespace Drupal\example\Controller;

use Drupal\Core\Controller\ControllerBase;

/**
 * Class DefaultController.
 */
class DefaultController extends ControllerBase {

Dear, I have a problem and I ask for help, please: My site in Drupal 8 is in maintenance mode and I can not enter to administer the site. If you try to access http://sandubacarioca.com.br/user/login besides not displaying the login form, it displays the following message: Skip to main content. Thank you!

I want to display content contributed by a user on their user profile page using a view. What settings do I adjust? I would like to display images, videos, blog posts, and other content.

Hello. I'm trying to render a (Full HTML) block programmatically inside a controller. The block body contains basic HTML tags like <p>Hello World</p>, and renders ok when not loaded programmatically.

$bid = 1; // Existing block created via UI.
$block = \Drupal\block_content\Entity\BlockContent::load($bid);
$build['my_block'] = $this->entityTypeManager()->getViewBuilder('block_content')->view($block);

return $build;

The rendered result prints the HTML tags:

I am rebuilding my website in Drupal 8. We used Simplenews in Drupal 7 for sending newsletters. Simplenews is still the first hit when searching for modules for newsletters. Is it still the way to go?

I understand Simplenews requires Mime Mail in D7 and Swiftmailer in D8. Swiftmailer requires the Mail System module. What is the difference?

I am rebuilding my website in Drupal 8. Is it correct that HTTPS rewriting is not included in the default .htaccess file?