Issue #3462559 by DYdave: Link to "Block" content overview page not displayed

    // If module block_content is enabled.

    if ($this->moduleHandler->moduleExists('block_content')) {

      $links['block_content.add_page'] = [

        'title' => $this->t('Add custom block'),

      // Add the custom blocks management under Content.

      $links['block_content_page'] = [

        'title' => $this->t('Blocks'),

        'route_name' => 'entity.block_content.collection',

        'parent' => 'system.admin_content',

      ] + $base_plugin_definition;

      $links['add_block'] = [

        'title' => $this->t('Add content block'),

        'route_name' => 'block_content.add_page',

        'parent' => 'block.admin_display',

        'parent' => $base_plugin_definition['id'] . ':block_content_page',

      ] + $base_plugin_definition;

      $links['entity.block_content.collection'] = [

        'title' => $this->t('Custom block library'),

        'route_name' => 'entity.block_content.collection',

        'parent' => 'block.admin_display',

      // Adds links for each block_content type.

      foreach ($this->entityTypeManager->getStorage('block_content_type')->loadMultiple() as $type) {

        $links['block_content.add.' . $type->id()] = [

          'route_name' => 'block_content.add_form',

          'parent' => $base_plugin_definition['id'] . ':add_block',

          'route_parameters' => ['block_content_type' => $type->id()],

          'class' => 'Drupal\admin_toolbar_tools\Plugin\Menu\MenuLinkEntity',

          'metadata' => [

            'entity_type' => $type->getEntityTypeId(),

            'entity_id' => $type->id(),

          ],

        ] + $base_plugin_definition;

      }

      if (version_compare(\Drupal::VERSION, '10.1', '<')) {

        // Add custom block types management under Structure.

        $links['entity.block_content_type.collection'] = [

          'title' => $this->t('Block types'),

          'route_name' => 'entity.block_content_type.collection',

          'parent' => 'block.admin_display',

        ] + $base_plugin_definition;

      }

    }

    // If module Contact is enabled.

    if ($this->moduleHandler->moduleExists('contact')) {