iMovie 10.1.9 represents a specific era of macOS (around High Sierra). Users often seek this exact version via torrents because: Hardware Compatibility

: Since Apple does not officially provide a "repository" of legacy versions for direct download, the "grey market" of torrenting becomes a tempting alternative for those trying to keep vintage hardware functional. The Risks of the "Free" Route

Rather than risking a system infection for a legacy version of iMovie, users have safer paths: The Mac App Store "Purchased" Tab