Because the software is no longer supported and the modern macOS file system (APFS) handles file fragmentation automatically, searching for a "2.1.1 license key link" often leads to significant security risks.
Since the software is legacy, you generally no longer need a paid license key for the older versions. Below is a review of iDefrag 5 (the final major version) and information regarding its current status. 💿 iDefrag Review: Legacy Disk Optimization idefrag 211 license key link