Cook the bacon slices in a large skillet over medium heat until crispy, about 6-8 minutes. Transfer to a paper towel-lined plate to drain and cool. Once cooled, crumble the bacon and set aside.
Place the peeled and diced potatoes, chopped onion, and minced garlic into the slow cooker.
Pour in the chicken broth and stir to combine. Add salt, black pepper, and smoked paprika.
Cover and cook on low for 6 hours, or until the potatoes are very tender.
Using a potato masher or immersion blender, mash or blend the soup slightly in the slow cooker, leaving some chunks for texture.
Stir in the whole milk, shredded cheddar cheese, sour cream, and unsalted butter until the cheese is melted and the soup is creamy.
Taste and adjust seasoning with additional salt and pepper if needed.
Serve the soup hot, garnished with crumbled bacon and sliced green onions.