Link by internal path in *.links.menu.yml not visible in admin menu
It seems to be necessary to use a route_name for this. Then you can control permissions and the internal link is visible for the editor role too:

1 – Change my_module.links.menu.yml to use a route_name instead of the url:

my_module.test_link:
  title: 'TEST LINK internal'
  route_name: my_module.test_route
  description: 'TEST internal'
  parent: system.admin_content
  weight: 99


2 – Add the route with  permission to my routing file my_module.routing.yml:

my_module.test_route:
  path: '/node/add'
  requirements:
    _permission: 'access content'