Prepare the cabbage by removing outer leaves, cutting in half, removing the core, chopping into bite-sized pieces, and rinsing under cold water.
In a large skillet, heat olive oil over medium heat. Add sliced onion and sauté for about 5 minutes until translucent. Stir in minced garlic and cook for an additional 1-2 minutes until fragrant.
Add chopped cabbage to the skillet with sautéed onion and garlic. Sprinkle in salt, black pepper, and red pepper flakes if using. Stir well to coat the cabbage.
Pour in the non-alcoholic ale and bring to a gentle simmer. Cover and cook for about 10-15 minutes until the cabbage is tender. Stir occasionally.
Remove the lid and stir in apple cider vinegar. Cook uncovered for another 2-3 minutes to reduce the liquid slightly.