https://phpstan.org/r/b8b34edb-7d22-4477-a1a7-4aa532d81c24

This is a pretty common way to forbid cloning the object in PHP: https://github.com/search?q=%22private+function+__clone%28%29%22&type=Code

IMO this shouldn't be reported as unused. It's like private function __construct() in singletons.