In previous releases, a "Legacy" build was provided that offered compatibility on very old (macOS) systems -- as far back as macOS 10.9. This was achieved by dynamically downgrading certain dependencies (PyQt5, PyNaCl) at build-time to the last known supported version. Recent updates to various dependencies (including autobahn, cryptography and python itself), however, have made maintaining such deep backward-compatibility increasingly more difficult and burdensome. In addition, because very few users (if any) still use such antiquated systems, and because such systems no longer receive security updates, support "Legacy" systems/builds should be discontinued.