Please add the ability to right click the file title at the top of the Affinity window to see the finder path of the file. This is a very useful feature and pretty much standard on current Mac OS apps.
I just thought of a way to do this with a pixel layer. It's kinda obvious once you get the "Aha!" moment.
Select the shape you want to stroke and create a new layer. Fill the new layer with white (or any other color for that matter; it just needs to be different from the Stroke).
Define the Stroke (as if stroking a path) using FX > Stroke. With a white Fill, use a black Stroke. Make a copy of this layer if you think you may need to make adjustments.
Rasterize the layer, then select the fill color and delete it. Voila! You've now got a stroked path!
It's kind of a kludge, but it works! :-)