Step 1: In a large mixing bowl, gently combine the ground beef, breadcrumbs, milk, egg, chopped onion, minced garlic, 2 tablespoons of ketchup, Worcestershire sauce, Italian seasoning, salt, and pepper. Mix just until everything is incorporated, being careful not to overmix.
Step 2: Form the meat mixture into a loaf shape, approximately 7-8 inches long and 4-5 inches wide. It should fit comfortably inside your Instant Pot.
Step 3: Pour 1 cup of beef broth or water into the bottom of your Instant Pot liner. Place a trivet inside the pot.
Step 4: Carefully place the formed meatloaf on top of the trivet. If desired, you can create a foil sling to make lifting easier.
Step 5: In a small bowl, whisk together the remaining 2 tablespoons of ketchup, brown sugar, and apple cider vinegar to create the glaze. Spread half of this glaze evenly over the top of the meatloaf.
Step 6: Secure the Instant Pot lid and set the vent to sealing. Select the "Manual" or "Pressure Cook" setting and cook on High pressure for 25 minutes.
Step 7: Once cooking is complete, allow for a Natural Pressure Release (NPR) for 10 minutes. After 10 minutes, carefully quick release any remaining pressure.
Step 8: Open the lid and carefully remove the meatloaf using the trivet handles or foil sling. Transfer it to a cutting board and spread the remaining glaze over the top. Let the meatloaf rest for 5-10 minutes before slicing and serving. This allows the juices to redistribute, ensuring a tender and moist result.