Lightroom 6 (v6.14) was the final perpetual license version ever released.
Adobe for purchase as a standalone (perpetual license) product. Adobe transitioned Lightroom exclusively to a subscription-based model via Adobe Creative Cloud in late 2017. Key Status Details how to buy lightroom 6 standalone
Adobe ceased all updates, including bug fixes and new camera support, for Lightroom 6 at the end of 2017. Lightroom 6 (v6