Nevermind, I’m dumb. This was what I ended up doing:
function my_relationship_query( $args, $field, $post_id ) {
// order by newest posts first
$args['orderby'] = 'date';
$args['order'] = 'DESC';
// return
return $args;
}
// filter for every field
add_filter('acf/fields/relationship/query', 'my_relationship_query', 10, 3);