Of course you know I love vignettes at the edges of maps. They help draw our eyeballs in to the focus area. So naturally I’d also love a vignette effect for area of interest polygons—not just around the perimeter of a layout, but a nice soft edge to a specific geographic shape.
So, here is an ArcGIS Pro style containing great big fat hack polygon symbol to give a feathered/blurry/soft edge sort of thing for your Area of Interest Overlay polygons.
Happy Mapping! John
P.S. If you’d like a more detailed description of the hole-punching cookie-cutting process, find a more long-winded version of this resource, with more examples, here.