Affinity Designer V2.1, does NOT do autotrace conversion of pixels into vectors. It can be done manually, or by some other programs.
https://www.youtube.com/watch?v=480dGcU6ce4
https://forum.affinity.serif.com/index.php?/topic/130625-png-to-vector/

Auto Trace in other programs takes many seconds to do.
Vector Magic ($), Inkscape, and SVG trace can do auto trace of PNG pixels.

- Brian