og_sm-8.x-1.0/og_sm_content/og_sm_content.site_links.menu.yml

og_sm.site_content:
  title: 'Content'
  route_name: og_sm.site_content
  menu_name: og_sm_admin_menu
  parent: og_sm.site.admin
  options:
    attributes:
      class:
        - 'toolbar-icon-system-admin-content'

og_sm.site_content.add_page:
  title: 'Add content'
  route_name: og_sm.site_content.add_page
  menu_name: og_sm_admin_menu
  parent: og_sm.site_content