OpenLiteSpeed does not support the PHP-FPM handler because it has its own built-in PHP handler, called LSPHP. LSPHP is designed to work specifically with OLS/LSWS and is optimized for performance and security.
PHP-FPM is a general-purpose PHP handler that can be used with any other web server. It is popular for its flexibility and scalability, but it can be more complex to configure and manage than LSPHP.
LSWS engineers decided to focus on developing and improving LSPHP rather than supporting PHP-FPM. This allows them to provide the best possible performance and security for users. Overall, LSPHP is a good choice for users who want the best possible performance and security.