Lightly spray the inside of the slow cooker with vegetable oil.

In a microwave-safe bowl, mix together the chopped onion, minced garlic, vegetable oil, 1 teaspoon of salt, and red pepper flakes. Microwave the mixture, stirring occasionally, until the onion softens, about 5 minutes. Transfer this softened mixture to the prepared slow cooker.

Add the collard greens and chicken broth to the slow cooker, ensuring they are well combined. Place the ham hock in the center of the greens.

Cover the slow cooker and cook until the collard greens are tender, either on low for 9 to 10 hours or on high for 6 to 7 hours.

Once the greens are cooked, transfer the ham hock to a cutting board. Let it cool slightly, then use two forks to shred it into bite-size pieces. Remove any excess fat, skin, and bones.

Stir the shredded ham and cider vinegar into the collard greens mixture.

Season the dish with salt, pepper, and additional cider vinegar to taste.