Lay two sheets of foil in a cross pattern inside the slow cooker and grease lightly so the loaf releases easily (visual cue: foil sling covers the base area).

In a large mixing bowl, combine ground beef, breadcrumbs, eggs, whole milk, grated small onion, minced garlic, Worcestershire sauce, Italian seasoning, garlic powder, salt, and pepper until evenly mixed (visual cue: mixture looks cohesive with no dry pockets).

Shape the mixture into a loaf and place it on the foil sling, centered so it cooks evenly (visual cue: loaf sits snug and level).

Mix ketchup, brown sugar, and apple cider vinegar, then spread half over the top of the meatloaf (visual cue: a glossy red layer covers the surface).

Cover and cook on Low for 5–6 hours (or High for 2.5–3 hours) until the internal temperature reaches 160°F (visual cue: edges look cooked and the center steams through).

Spread the remaining glaze over the top and cook on High for 20 minutes until set (visual cue: glaze darkens and clings thickly).

Lift the meatloaf out using the foil sling and transfer to a cutting surface (visual cue: steam rises as it clears the crock).

Rest the meatloaf for 10 minutes before slicing so juices settle (visual cue: surface firms slightly and won’t run as much).

Slice and serve (visual cue: a moist, tender interior with glaze on top).