rovo79

<?php

namespace Drupal\mymodule;

use Drupal\Core\File\Exception\FileNotExistsException;
use Drupal\Core\File\FileSystemInterface;
use Drupal\file\FileRepositoryInterface;
use Drupal\Core\Logger\LoggerChannelFactoryInterface;
use Drupal\Core\Logger\LoggerChannelInterface;

rovo79

Render custom blocks

$bid = 'myblock';
$block = \Drupal\block_content\Entity\BlockContent::load($bid);
$render = \Drupal::entityTypeManager()->getViewBuilder('block_content')->view($block);

Render plugin blocks

$block_manager = \Drupal::service('plugin.manager.block');