Get rendered content of one block created as derivative block I have created derivative blocks using a method such as this and want to get the contents of a specific derivative block.

I can see all the available blocks (even derivative blocks) that have been assigned to a region with 

 $ids = \Drupal::entityQuery('block')-&gt;execute();


but can't see unassigned blocks 

I have a feeling that I need to use the code from berdir's answer b)

$variables['block_output'] = \Drupal::service('plugin.manager.block')
   -&gt;createInstance($plugin, $configuration)
   -&gt;build();


but don't know what to use for $plugin or $configuration

any help example will be appreciated
It sems this will do the trick:

  $blockManager = \Drupal::service('plugin.manager.block');
  //see all available block plugins (even not instantiated)
  $contextRepository = \Drupal::service('context.repository');
  $definitions = $blockManager-&gt;getDefinitionsForContexts($contextRepository-&gt;getAvailableContexts());


Here is how I used this info:

function TEMPLATE_preprocess_node(&amp;$vars) {
  $blockManager = \Drupal::service('plugin.manager.block');   
  $vars['content']['derivative_block'] = $blockManager-&gt;createInstance('module_name:block_derivative_id')-&gt;build();
}


If you enable the commented lines $definitions will get you all available blocks 

Credit goes out to enzo for this solution.

More info about programmatic block placement.