Pat the beef dry and toss it with the flour, salt, and pepper in a bowl until evenly coated.
Heat the olive oil in a large skillet over medium-high heat. Add the beef and brown it on all sides, working in batches if needed.
Transfer the browned beef to the slow cooker. Add the onion, carrots, butternut squash, garlic, and tomato paste.
Pour in the beef broth and stir to combine everything. Sprinkle in the chopped sage.
Cover and cook on low for 8 hours until the beef is tender and the gravy has thickened.
Taste and adjust salt and pepper before serving.