Prepare the Roast:
Pat the roast beef dry with paper towels. Season generously with garlic powder, onion powder, smoked paprika, thyme, salt, and pepper.
Sear the Roast:
Heat olive oil in a skillet over medium-high heat. Sear the roast on all sides until browned, about 2–3 minutes per side.
Transfer to Slow Cooker:
Place the seared roast in the slow cooker.
Make the Balsamic Glaze:
In a small saucepan, combine balsamic vinegar, brown sugar, soy sauce, minced garlic, and red pepper flakes (if using).
Cook over medium heat, whisking constantly, until the sugar dissolves and the glaze thickens slightly, about 3–4 minutes.
Cook the Roast:
Pour half of the balsamic glaze over the roast in the slow cooker. Reserve the remaining glaze for later.
Cover and cook on low for 8–10 hours or on high for 4–6 hours, until the beef is fork-tender.
Glaze and Serve:
Once the roast is done, shred it with two forks or slice it, as preferred. Drizzle the reserved balsamic glaze over the meat before serving.