pm-4.1.x-dev/modules/pm_sub_task/pm_sub_task.links.action.yml

pm_sub_task.type_add:
  title: 'Add Sub Task type'
  route_name: entity.pm_sub_task_type.add_form
  appears_on:
    - entity.pm_sub_task_type.collection

pm_sub_task.add_page:
  title: 'Add Sub Task'
  route_name: entity.pm_sub_task.add_page
  appears_on:
    - entity.pm_sub_task.collection
    - view.pm_sub_task.collection
    - entity.pm_task.canonical