Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and sauté for about 5 minutes, or until translucent.
Stir in the minced garlic and red pepper flakes, cooking for another minute until fragrant.
If using, add the smoked ham hock or turkey neck to the pot for additional flavor.
Pour in the chicken or vegetable broth and bring to a simmer.
Once simmering, add the chopped collard greens to the pot. Stir well to ensure the greens are submerged in the broth.
Season with salt and black pepper, then cover and cook on low for about 30-40 minutes, stirring occasionally, until the collard greens are tender.
Once the greens are cooked, stir in the apple cider vinegar and adjust the seasoning as needed.
Remove the ham hock or turkey neck, if used, and shred any meat to add back to the greens if desired.
Serve warm as a hearty side dish alongside your favorite main courses.