Pat the chuck roast dry with paper towels and season all sides with salt, pepper, garlic powder, onion powder, paprika, thyme, and rosemary.
Heat olive oil in a skillet over medium-high heat. Sear the roast for 3–4 minutes per side until browned.
Place sliced onions, garlic, and radishes into the slow cooker.
Add the seared roast on top of the vegetables.
Pour in beef broth and Worcestershire sauce. Add bay leaves and butter.
Cover and cook on LOW for 8–9 hours or HIGH for 4–5 hours until the beef is fork-tender.
Remove the roast and radishes from the slow cooker. Discard bay leaves.
For the gravy, strain the cooking liquid and return it to a saucepan. Simmer and whisk in butter and xanthan gum until slightly thickened.
Slice or shred the pot roast and serve with radishes topped with keto gravy.
Garnish with fresh parsley before serving.