commerce-8.x-2.8/modules/order/commerce_order.links.action.yml

entity.commerce_order.add_page:
  route_name: entity.commerce_order.add_page
  title: 'Create a new order'
  appears_on:
    - entity.commerce_order.collection

entity.commerce_order_type.add_form:
  route_name: entity.commerce_order_type.add_form
  title: 'Add order type'
  appears_on:
    - entity.commerce_order_type.collection

entity.commerce_order_item_type.add_form:
  route_name: entity.commerce_order_item_type.add_form
  title: 'Add order item type'
  appears_on:
    - entity.commerce_order_item_type.collection