Combine salt, pepper, smoked paprika, garlic powder, onion powder, and cayenne. Pat brisket completely dry with paper towels and rub seasoning all over every surface.
Heat olive oil in a large skillet or cast iron pan over medium-high heat until shimmering. Sear brisket fat-side down for 5–6 minutes until a deep mahogany crust forms. Flip and sear the other side for 4–5 minutes. Transfer to the crockpot fat-side up.
In the same skillet, reduce heat to medium and add the onions. Cook for 5–6 minutes until softened. Add garlic and tomato paste and stir for 2 minutes. Pour in the red wine and scrape up all browned bits from the pan. Simmer for 2 minutes.
Add crushed tomatoes, beef broth, Worcestershire sauce, brown sugar, apple cider vinegar, bay leaves, and thyme to the skillet. Stir to combine, then pour the entire sauce over the brisket in the crockpot.
Place the lid on the crockpot and cook on LOW for 8 hours. The brisket is ready when it reaches 200–205°F internally and a fork slides in with zero resistance.
If making homemade BBQ sauce, whisk all ingredients in a small saucepan over medium-low heat and simmer for 10 minutes until thickened. Set aside.
Preheat oven to 425°F. Carefully transfer the brisket from the crockpot to a foil-lined baking sheet. Brush generously with BBQ sauce on all sides, paying extra attention to the fat cap.
Bake uncovered for 12–15 minutes until the glaze is bubbling and caramelized at the edges. For extra char, broil for the final 2–3 minutes — watch it closely.
Rest brisket loosely tented with foil for 15–20 minutes. Discard bay leaves and thyme from the crockpot liquid and reduce on the stovetop if desired. Slice against the grain and serve with the braising sauce and extra BBQ sauce on the side.