Creating a Post, can authors be ordered by last name?

When I create a post, the author dropdown/select seems to order authors by the first letter of the full display name.

Is there a bit of code for functions.php that would order this dropdown by last name?

Here’s one example how we can modify the order of users in the dropdowns on the post.php and post-new.php pages (PHP 5.4+):

/**
 * wp_dropdown_users - modify ordering on post.php and post-new.php
 */
add_filter( 'wp_dropdown_users_args', function( Array $query_args, Array $args )
{
    // Nothing to do if we're not on post.php and post-new.php
    if( ! did_action( 'load-post.php' ) && ! did_action( 'load-post-new.php' ) )
        return $query_args;

    // Modify the user query - Adjust to your needs!
    $query_args['meta_key'] = 'last_name';
    $query_args['orderby']  = [ 'meta_value' => 'ASC', 'display_name' => 'ASC' ];

    return $query_args;

}, 10, 2 );

Here we query users that have the last_name meta key and order first by the last_name and then display_name.

Hope you can adjust it to your needs!