Install
This is the repository archive. It installs, but the folder name will carry the branch suffix and updates will not flow.
Install straight from GitHub with WP-CLI:
wp plugin install https://github.com/payter/automatic-lower-level-menu-pages/archive/refs/heads/master.zipNo built-in updater. New versions won't appear under Dashboard → Updates. Install new releases yourself, or let Git Updater track the repository.
Automatic lower-level menu pages - Plugin for Wordpress
By default Wordpress will automatically add just top level pages, this plugin will add every level of pages to the menu.
Just install and activate this plugin and setup your menu with "Automatically add new top-level pages to this menu" setting checked.
Remember that this plugin will add only new pages to the menu, or pages that will change status to publish.