I'm using different page-templates this for pages.
Now I need the same for posts.
Since 4.7 this should be a core functionality.
So I pretty much followed this quick tutorial and added a custom single-duplicate.php in my theme folder and added this code at the top:
<?php
/*
Template Name: Full-width layout
Template Post Type: post, page, product
*/
However upon creating a new post I dont see the "Post Attributes" Box with the Template-dropdown. What do I do now? Is it possible that my theme somehow prevents that?
Here's my themes functions.php as a gist, if that helps.