Display a block drupal programmatically

Content blocks are blocks that you create in the interface. They are much like nodes configurable data structures, with fields etc. If you want to render one of these, you can do what you would normally do with entities, load them and render them with the view builder:

<?php

function blog_preprocess_page(&$vars)
{
    $block_manager = \Drupal::service('plugin.manager.block');
    $vars['myblock']= [
        '#type' => 'container',
        "element-content" => $block_manager->createInstance('id_block', [])->build(),
    ];
}

?>

and in the twig template:

{{ myblock }}