Heat olive oil and butter over medium-high in a large Dutch oven or heavy-bottomed cast-iron skillet.
Season the cubed stew meat with salt, black pepper, and Creole seasoning (if using). Add the seasoned meat to the pot.
Sear the meat, turning occasionally, until browned on all sides. That should take about 2 minutes per side.
Once the meat is browned, add the minced onion to the pot. Cook the onion, stirring occasionally, until it softens and becomes translucent, approximately 4-5 minutes.
Add the minced garlic and thyme. Cook for another minute, stirring frequently, until fragrant.
Pour a small amount of water into the pot to deglaze it, scraping up any browned bits from the bottom. Cook for about a minute.
Transfer the contents of the pot to a slow cooker.
Add the beef broth, bouillon powder, and Worcestershire sauce to the slow cooker. Stir to combine.
Cover the slow cooker and set it to cook on LOW for 6-7 hours or on HIGH for 3-4 hours. The beef is done when fork-tender and shreds easily.
Prepare the thickening mixture about 30 minutes before the cooking time is complete. In a small bowl, whisk the flour and water until smooth.
Stir it into the slow cooker, making sure it is well incorporated.
If the sauce is too thick, add more broth or water to reach your desired consistency.
Taste the sauce and adjust the seasoning to your preference with additional salt and black pepper.
Serve the beef stew over mashed potatoes, rice, or egg noodles.