There is no official documented list of all possible post meta keys in core. The closest I could for anything unofficial was this answer on Stack Exchange:
You probably don’t want to use the following post meta keys:
_thumbnail_id
– Used to store the featured image ID_edit_last
– Used by the Heartbeat API_edit_lock
– Used by the Heartbeat API_wp_page_template
– Stores the page template._wp_attached_file
_wp_attachment_metadata
_menu_item_{url, object, object_id, target, classes, xfn, ... }
as your custom meta keys, as they might be overwritten by the
WordPress Core.
However this is over 3 years old and not comprehensive. It’s only based on the answering user checking for all the keys in their database. You’ll notice that _wp_old_slug
is missing, for example.