Hello, I have made this set to 0, but when a reply is deleted, it is supposed to disappear for good but it is still shown as a hidden post, and when I click to expand it, it is shown in red.
How do I make the deleted post disappear completely?
it is deleted - for your users. only mods and admins (staff) can see deleted posts indicated in orange. records in Discourse are rarely ever permanently deleted, but it is possible. that delete removed posts after setting is the author delete setting - if a regular user deletes a post how long until it is permanently deleted for them.
note: if you ever need to restore a deleted post (orange highlighted) , you should be able to click the dots below the post to get to the undo icon. it will be hidden so you will have to unhide it by clicking “view 1 unhidden reply” before you can restore it.
As Lilly says, when clicking on the dustbin icon the post will be soft-deleted (that is, only visible to admins and mods[1]). The delete removed posts after time is how long a user has the option to ‘undelete’ their post and reverse their decision before it becomes visible to only admin/mods.
To hard-delete a post you would need to enable the hidden site setting can_permanently_delete, which would allow an admin to permanently delete that post from the database with no means to restore it.