One more addition. If you need to setup non-thread-safe PHP on XAMPP/Apache to use loadextension, look at this article:
RollingHog ¶5 years ago
For newbies like me: if loadExtension fails with "Not supported in multithreaded Web servers" message (which always happens on IIS and sometimes - on Apache), you need to use non-thread-safe build of PHP, which is not always a bad idea; see https://www.geeksforgeeks.org/what-is-thread-safe-or-non-thread-safe-in-php/