Heat the olive oil in a large skillet over medium-high heat. Add the beef and brown it on all sides for about 5 minutes, then transfer the meat to the slow cooker.
Add the potatoes, mushrooms, onion, and garlic to the slow cooker. Sprinkle the flour, salt, and pepper over the ingredients and stir to coat everything evenly.
Pour in the beef broth and add the thyme leaves. Stir once more to combine.
Cover and cook on low for 7 to 8 hours or on high for 4 hours, until the beef is fork-tender and the potatoes are soft.
Stir in the heavy cream during the last 15 minutes of cooking. Let the stew sit uncovered for a few minutes to thicken slightly before serving.