TRACK
I ran an extra kilometre because of three detours. The first one was my mistake after 2.5 km. I turned around and returned to the original path.
The second detour was after 13 km because I entered a private property (there was a fence). The last detour was after 19 km. I ended up on a dead-end path. I turned around and found the cycle path, which runs more or less parallel to the original GPX track. I would recommend taking this route directly if you are planning to attempt it.
The route is more "trail" in the next section: single track, small climbs and a lot of sand. The second part is more "road running": long, straight paved roads. I wore road running shoes. There's no particular need for trail running shoes. The first part is sandy but never muddy (neither in December, like in my case).
PERFORMANCE
I ran this FKT with no specific preparation (I'm in the off-season; in a month's time, I'll start training for a marathon). I didn't have any specific goals other than to enjoy a nice day in a beautiful place. And it worked!
SUPPLIES
I took a soft flask containing half a litre of water and another soft flask containing half a litre of water mixed with 300 grams of carbohydrates. I also had two sweet snacks (nougats).
I didn't see any fountains on the route, so I would strongly recommend bringing more water if you attempt this FKT in the warmer months.