Heat a large skillet over medium-high heat and add olive oil. When shimmering, add the beef chunks and sear until browned on all sides, about 5 minutes, to develop flavor. Transfer the browned beef to the slow cooker.
In the same skillet, toss in the sliced onions and cook until they soften and turn golden brown, about 8 minutes, stirring occasionally to prevent sticking. Scrape up any browned bits from the pan to add depth to the flavor, then transfer the onions to the slow cooker.
Add the minced garlic and smoked paprika to the skillet, cooking for about 1 minute until fragrant. Stir to evenly distribute the smoky aroma, then pour this mixture into the slow cooker.
Pour the beef broth into the slow cooker, then add the rinsed barley and season with salt and pepper as desired. Give everything a gentle stir to combine all flavors evenly.
Cover the slow cooker with its lid and set to low heat. Let it simmer for about 4 hours, or until the beef is tender and easily shredded, and the barley is soft but still chewy.
Once cooked, open the lid and stir the soup gently. Taste and adjust seasoning with more salt, pepper, or smoked paprika if needed. The broth should have thickened slightly, and the ingredients will be harmoniously tender.
Spoon the hot, fragrant soup into bowls and serve immediately, enjoying the rich aroma and comforting textures of the tender beef and chewy barley. Perfect for a cozy meal on a chilly day.