block_content.links.action.yml

block_content_type_add:
  route_name: block_content.type_add
  title: 'Add block type'
  appears_on:
    - entity.block_content_type.collection

block_content_add_action:
  route_name: block_content.add_page
  title: 'Add content block'
  appears_on:
    - block.admin_library
    - entity.block_content.collection
  class: \Drupal\block_content\Plugin\Menu\LocalAction\BlockContentAddLocalAction