In cases like this, the theft can also be reported to search engines which will impact their ranking as well as remove the direct search result in cases when they refuse to remove the infringing content.
Outside of that, a common tactic used by freeware developers is to add an install (for applications that require installation ) or first time run note indicating the official sources and warning that if they purchased or acquired the freeware from an unofficial source then they were scammed and likely got a version bundled with malware. It often works since it is a very real risk since malware devs often focus on bundling malware with the launchers for legit software.
Often that throws enough doubt and raises enough red flags on 3rd parties trying to monetize your hard work for their own gain.