$args = array(
    'post_status' => array( 'publish', 'draft')
);
$query = new WP_Query( $args );

add_action( 'pre_get_posts', function ( $q )
{
    if (    $q->is_main_query() // Target main query only
         && $q->is_single() // Only target single posts, can use is_singular as well
    ) {
        $q->set( 'post_status', array( 'publish', 'draft' );
    }
});