Trim any visible fat from the beef stew meat and pat dry with a paper towel.
Heat the olive oil in a large skillet over medium-high heat and sear the beef until browned on all sides.
Transfer the browned beef to a slow cooker.
In the same skillet, add the diced onion, minced garlic, and chopped red bell pepper, sautéing for 3 minutes until slightly softened.
Stir the smoked paprika into the vegetables for 30 seconds to release the oils, then transfer everything to the slow cooker.
Add the diced potatoes, tomato sauce, and beef broth to the slow cooker, stirring to combine.
Cover and cook on low for 6 to 8 hours (or high for 3 to 4 hours) until the beef is tender.
Stir in the apple cider vinegar, sea salt, and black pepper just before serving to brighten the flavors.