You can add multiple compared condition variable in single if condition using logical OR operator.
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function force_type_private($post)
{
if ($post['post_type'] == 'my_post_type1' || $post['post_type'] == 'my_post_type2') {
$post['post_status'] = 'private';
}
return $post;
}
add_filter('wp_insert_post_data', 'force_type_private ');