By 2018, Autodesk gave up on the desktop market entirely, making SketchBook free to download. But free meant no updates, no vector, and eventually, removal from the App Store in 2022.

SketchBook Designer - Concept Design & Illustration Software - Autodesk

Why not just use the new SketchBook (now discontinued by Autodesk) or Procreate? Because Designer 2013 had unique tools that modern apps dropped.