You can also use the Twig Field Value module (https://www.drupal.org/project/twig_field_value) And then you can use this snippet: {{ file_url(content.field_block_background_image|field_target_entity.field_media_image.entity.uri.value) }}
You can also use the Twig Field Value module (https://www.drupal.org/project/twig_field_value)
And then you can use this snippet: