Season the beef cubes with salt and pepper. Heat a skillet over medium-high heat and brown the beef in batches until all sides are seared. Transfer the beef to the slow cooker.
Add the potatoes, carrots, onion, and garlic to the slow cooker with the beef.
In a small bowl, whisk the flour into 1/2 cup of the beef broth until smooth. Pour this mixture into the slow cooker along with the remaining broth, balsamic vinegar, and thyme.
Stir everything gently to combine. Cover and cook on low for 8 hours or until the beef is fork-tender and the gravy has thickened.
Taste and adjust salt or pepper if needed before serving.