Pat the roast dry and season. Blot the chuck roast with paper towels.
Mix salt, black pepper, garlic powder, onion powder, dill, parsley, and chives. Rub the mixture all over the roast.
Sear for flavor. Heat avocado oil in a heavy skillet or Dutch oven over medium-high heat. Sear the roast 3–4 minutes per side until deeply browned.
This builds the savory crust and boosts the sauce.
Layer ingredients. Place the roast in a slow cooker or leave it in the Dutch oven. Add beef broth, pepperoncini brine, and apple cider vinegar (if using). Scatter the pepperoncini around the meat and top with the butter.
Cook low and slow. For a slow cooker, cook on Low for 8–9 hours or High for 4–5 hours.
For the oven, cover the Dutch oven and cook at 300°F (150°C) for 3–4 hours. The roast is done when it shreds easily with a fork.
Shred and return to juices. Transfer the roast to a cutting board and shred with two forks. Skim excess fat from the top of the cooking liquid if desired, then return the shredded beef to the pot and toss to coat.
Adjust seasoning. Taste and add salt or pepper as needed.
If you like more tang, splash in extra pepperoncini brine. For heat, sprinkle in crushed red pepper flakes.
Serve. Spoon over mashed cauliflower, roasted green beans, sautéed cabbage, or zucchini noodles. Garnish with chopped parsley for a fresh finish.