Season the beef with salt and pepper, then place it in your crockpot with onions and garlic.
Whisk cranberry sauce, vinegar, broth, sugar, soy sauce, thyme, and pepper together.
Pour mixture over beef. Cover and cook on LOW for 8 hours or HIGH for 4 hours.
Shred beef with forks and stir into sauce.
Serve warm with mashed potatoes or roasted vegetables.
