page_layouts-1.0.1/page_layouts.links.menu.yml

entity.page_layouts_layout.settings:
  title: 'Layouts'
  description: 'Configure a Layout entity type.'
  route_name:  entity.page_layouts_layout.settings
  parent: system.admin_structure

entity.page_layouts_layout.collection:
  title: 'Layouts'
  description: 'List of layouts.'
  route_name: entity.page_layouts_layout.collection
  parent: system.admin_content