WP_QUERY order posts by two combined meta_value dates

Question

On post insert/update, set the post’s menu_order as the maximum of the numeric MMDD values of original_date and featured_date. Maybe set the menu order in the format 1MMDD to avoid a leading zero.

Then we can order the custom type posts by the menu order very fast with:

WP_Query( [ 
   'post_type' => 'custom_post_type', 
   'orderby'   => 'menu_order', 
   'order'     => 'DESC' 
] );

where menu_order is a int(11) column in the posts table.

If not all of the custom type posts have these custom dates, group them e.g. by a custom taxonomy, to use in your WP_Query. Maybe one could instead look for posts with non-zero menu order.