In a medium bowl or large measuring cup with a spout, whisk together the sauce ingredients: broth, vinegar, maple syrup, soy sauce, garlic, and cinnamon. Keep near the stove.
In the bottom of a 6-quart or larger slow cooker, scatter the onion. Top with the carrots, potato, and apple.
In a small bowl, combine the cornstarch, salt, thyme, and black pepper. Rub all over the outsides of the pork, pressing as much to adhere as you can.
In a large cast iron or similar sturdy-bottomed skillet, heat the oil over medium high. Once the oil is hot and shimmering (make sure it’s hot!), add the pork. Sear on all sides until golden, about 2 minutes per side. Place on top of the vegetables in the crockpot, nestling it down inside them slightly.
Return the skillet to medium heat. Pour in the sauce mixture (be careful, it will splatter). With a wooden spoon or rubber spatula, scrape up any browned bits of pork stuck to the pan (this is FLAVOR). Let simmer, stirring constantly, for 1 minute. Pour over the pork.
Cover and cook the pork on LOW for 2 to 3 hours, until it reaches an internal temperature of 135 to 140 degrees on an instant read thermometer (pork is considered done at 145 degrees F. The carryover cooking during resting will bring it to temperature). Remove to a large serving plate. Cover and let rest.
While the pork rests, stir together the vegetables, apples, and sauce in the crockpot. Cover and turn the heat to HIGH. Let continue cooking until the vegetables are tender, about 20 minutes more.
Cut the pork crosswise into slices of desired thickness. Serve with the vegetable mixture with the cooking liquid spooned over the top.
TO STORE: Refrigerate pork roast and vegetables in an airtight storage container for up to 3 days.
TO REHEAT: Gently rewarm leftovers in a baking dish in the oven at 350 degrees F or in the microwave.
TO FREEZE: Freeze pork roast and vegetables in an airtight freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.