Preheat oven to 425°F (220°C).
Trim Brussels sprouts and remove damaged outer leaves.
Halve sprouts lengthwise; quarter unusually large ones.
Dry thoroughly.
Cut bacon into approximately ½-inch pieces.
Toss Brussels sprouts with olive oil, salt, and black pepper on a large sheet pan.
Scatter raw bacon pieces among the sprouts.
Turn as many sprouts as possible cut-side down.
Roast for 18 minutes.
Whisk maple syrup, Dijon mustard, garlic, and thyme.
Remove pan from oven and turn the sprouts and bacon.
Drizzle with maple-Dijon mixture and toss.
Return to oven for 7–10 minutes, until sprouts are caramelized and bacon is cooked and crisp.
Remove from oven and drizzle with apple cider vinegar.
Toss gently.
Taste and adjust seasoning.
Finish with fresh thyme and serve warm.