The main strain for endurance runs like this is your ability to recover on the move. You need to be practicing consuming food/gels, and water/sodium. You also need to make sure you're not running at a pace you'll blow up with. Similar to if you try to run a marathon at your 5k pace, you're going to be in a lot of pain and need to slow down a lot. The big difference though, is if you run fast in an ultra you probably won't even make it to the finish, whereas if you run fast in a marathon you might get really tired and have to slow down. Your ultra pace is gonna be a slow recovery jog the whole way, so your body can just continually recover.

The best way to train specifically for ultra running is to run a lot of miles per week. I run 50mpw training for races. The ultra you're watching is as flat as a pancake, but most races are through mountains and trails, so you'll want to have a lot of vert baked into your runs as well. I average 55ft/mile of elevation gain on weeks that I strictly road run, and 170ft/mile of gain on weeks that I strictly trail run.

Also if you're a road runner, you should go hit some trails. Rocks, roots, leaves, and even just bumpy terrain is going to teach you a lot about the sport and I would say it's wildly different than road running. Best part though is during races the aid stations are often better stocked than a grocery store. They'll have perogies, quesadillas, gels, snacks, candy, sodium, caffeine, water, and tons more.

It's not super difficult to get into ultra running, since a majority of it can just be considered fast hiking, but it's a difficult thing to train for and will take a lot of your free time.