You have two options: either do what you think is best or follow the manufacturer’s recommendations. Perhaps a third option would be to do a mix of the first two.
If you’re not sure (conservative mode), I would follow the manufacturer’s recommendations, as they surely know much more about their product than most people on this forum. This way, you can also ask for support with more confidence if, unfortunately, something goes wrong with your design.
Getting back to the matter at hand… If you want to replicate the suggested layout, simply grab a net-tie from the kicad symbol library, place it in the schematic connecting AGND and PGND, assign a net-tie footprint and continue with the layout routing. You will have AGND and PGND nets in order to create respective zones/islands.
Yes there are some stuff about this here
and here