actualBounds returns same width of object regardless of zoom level

When trying to retrieve an objects’ recalculated width the same width is returned regardless of zoom level.

This happens when listening for the ChangedSelection event like so:
e.diagram.selection.first().actualBounds.width

Same width in both zoom levels

That is correct – all Part positions, locations, and sizes are in document coordinates. Discussion is at https://gojs.net/latest/intro/viewport.html

Perhaps you should multiply the Node.actualBounds.width by the Diagram.scale.