Hi,
I was also looking for a tool similar to the PS Polygonal Lasso, but Affinity's freehand tool doesn't really come up to my expectations, cause it lacks some precision (as you're not able to create straight lines - <shift> doesn't work).
So I tried the pencil instead. You can create a path with it and convert that into a selection afterwards. It's very similar to the PL but...
It's not possible (afaik) to add or substract any further selections that way like you can do with the PL.
It's a pity, but as long as Affinity doesn't offer that feature, I still have to use different programs for different work steps. :-(
