Hi @quirksmode
This is achievable through the use of the acf/fields/post_object/query filter. You can modify the $args array as follows:
function my_post_object_query( $args, $field, $post ) {
$args[‘author’]=$user_id
return $args;
}
add_filter(‘acf/fields/post_object/query/name=my_post_object’, ‘my_post_object_query’, 10, 3);
For more info you can refer to this article: acf/fields/post_object/query