Cook chopped bacon in a large skillet over medium heat until crispy. Remove half of the bacon and set aside.

Add sliced onion to the bacon drippings and cook until soft and lightly golden. Stir in garlic and cook until fragrant.

Add sliced cabbage to the skillet and toss with the onion, garlic, and bacon fat.

Season with salt, pepper, and red pepper flakes if using. Cook, stirring occasionally, until cabbage is tender and caramelized.

Return reserved bacon to the pan, add vinegar if desired, toss, and serve warm.