Preheat the oven to 425 degrees F (220 degrees C). Line a 10x15-inch baking sheet with aluminum foil.

Whisk maple syrup, 1 teaspoon olive oil, thyme, 1/4 teaspoon salt, and 1/4 teaspoon black pepper together in a small bowl until well combined. Set aside.

Toss sweet potatoes, Brussels sprouts, 2 teaspoons olive oil, 1/4 teaspoon salt, and 1/4 teaspoon black pepper together in a large bowl until evenly coated. Set aside.

Brush chicken with remaining 1 tablespoon olive oil; season with remaining 1/4 teaspoon salt and 1/4 teaspoon black pepper. Arrange chicken, skin-sides down, in center of the prepared baking sheet. Arrange sweet potato mixture around chicken.

Roast in the preheated oven for 15 minutes. Flip chicken; brush chicken, sweet potatoes, and Brussels sprouts with maple syrup mixture.

Continue roasting until sweet potatoes tender and chicken is no longer pink in centers and the juices run clear, about 15 minutes more. An instant-read thermometer inserted near but not touching bones should read at least 165 degrees F (74 degrees C).

Sprinkle with pecans and cranberries; serve.