Preheat the oven to 425°F and line a large rimmed baking sheet with parchment paper.
Toss the butternut squash, Brussels sprouts, apple, and red onion with 2 tablespoons olive oil, thyme, half the rosemary, salt, and pepper.
Spread the vegetables across the sheet pan, leaving space in the center for the chicken.
Pat the chicken thighs dry, rub with remaining olive oil, and season with salt, pepper, smoked paprika, garlic, and remaining rosemary.
Place the chicken among the vegetables, skin side up, and roast for 25 minutes.
Whisk the maple syrup, Dijon mustard, apple cider vinegar, and a pinch of salt to make the glaze.
Brush the chicken with half the glaze, stir the vegetables carefully, and roast for another 15 to 20 minutes, until the chicken reaches 165°F.
Broil for 2 to 3 minutes if desired for extra browning, then rest briefly, garnish with parsley, and serve.
