Preheat the oven to 425°F. Line a large sheet pan with parchment paper or lightly grease with avocado oil spray.
Add the potatoes to the sheet pan. Drizzle with 1 tbsp avocado oil and season with 1/2 tsp garlic powder, 1/2 tsp smoked paprika, 1/2 tsp dried thyme, 1/2 tsp salt, and the black pepper. Toss until evenly coated, then spread into a single layer.
Roast the potatoes for 15 minutes to give them a head start.
Meanwhile, pat the chicken thighs dry. Drizzle with the remaining 1 tbsp avocado oil and season with the remaining 1/2 tsp garlic powder, 1/2 tsp smoked paprika, 1/2 tsp dried thyme, and 1 tsp salt. Toss until evenly coated.
Remove the sheet pan from the oven and toss the potatoes. Add the seasoned chicken thighs, apple, and red onion to the pan, arranging everything in a single layer with some space between the ingredients. Toss the apple and onion lightly in the oil and seasonings already on the pan.
Return to the oven and roast for another 25-30 minutes, or until the chicken reaches an internal temperature of 165°F, the potatoes are golden and fork-tender, and the apples are lightly caramelized but still hold their shape. For extra browning, broil for the final 2–3 minutes, watching closely.
While the sheet pan finishes roasting, make the maple Dijon cream sauce. Add the butter to a small saucepan over medium heat. Once melted, add the garlic and cook for about 30 seconds, until fragrant.
Add the chicken stock, Dijon mustard, maple syrup, apple cider vinegar, and dried thyme. Whisk until smooth and bring to a gentle simmer. Cook for 2-3 minutes.
Reduce the heat to low and stir in the heavy cream. Gently simmer for another 3-5 minutes, stirring occasionally, until the sauce has slightly thickened. Season with salt and pepper to taste.
Drizzle the warm maple Dijon cream sauce over the roasted chicken, apples, onions, and crispy potatoes just before serving, or serve it on the side for spooning over each portion. Finish with fresh thyme, if desired.