How to get a custom post with the largest ID (not the last post by date)

Turns out, I was kind of wrong when I tried to get the largest ID. What I needed was to get posts by, and then to sort by, the order number itself! Here’s what I came up with:

$num_args = array(
    'post_type' => 'my_store_order',
    'post_status' => array('mystatus_1', 'mystatus_2', 'mystatus_N'),
    'numberposts' => 1,
    'meta_query' => array(
        'my_clause' => array(
            'key' => 'my_order_number',
            'type' => 'numeric',
            'compare' => 'EXIST'
        )
    ),
    'orderby' => 'my_clause',
    'order' => 'DESC'
);

Also, since post meta is a string, I added ‘type’ => ‘numeric’ so when being sorted it would be treated as a number (1,2,10 vs 1,10,2)

This post helped me a lot