The HTC HD Mini, launching with 6.5.3, was technically supported for a very short period, but the experience was dreadful.

If you are looking to revive your HTC HD Mini for communication purposes, WhatsApp is off the table. However, the device is not entirely useless.

The HTC HD Mini runs Windows Mobile 6.5. Microsoft eventually moved from Windows Mobile to Windows Phone 7, 8, and 10. These were completely different operating systems, incompatible with older apps. As support for Windows Mobile dried up, developers stopped updating their apps for the platform. Microsoft officially shut down the Windows Marketplace for Mobile years ago, meaning the official source for apps is now a ghost town.