In a large mixing bowl, add ground meat, breadcrumbs, milk, chopped onion, garlic, egg, ketchup, tomato paste, salt, pepper, paprika, and oregano. Mix gently using your hands or a spoon until everything is just combined. Do not overmix.
Form the mixture into a round or oval loaf shape. Keep it slightly loose and do not press too hard so the meatloaf stays soft after cooking.
Pour 1 cup water into the bottom of the Instant Pot insert. Place the metal trivet inside. This step is important to create steam for pressure cooking.
Place the shaped meatloaf on a foil sling or in a small heat-safe pan. Carefully lower it onto the trivet inside the Instant Pot.
Close the lid and set the valve to sealing. Cook on high pressure for 25 minutes. Once cooking is done, allow a natural pressure release for 10 minutes, then carefully release any remaining pressure.
Open the lid and check that the meatloaf is fully cooked. The internal temperature should reach at least 75 degrees Celsius.
In a small bowl, mix ketchup, brown sugar, and mustard until smooth.
Carefully remove the meatloaf using the foil sling. Place it on a baking tray and spread the glaze evenly on top.
Place the meatloaf under a hot oven broiler for 3 to 5 minutes until the glaze becomes glossy and slightly caramelized.
Let the meatloaf rest for 5 to 10 minutes before slicing. This helps it hold its shape and stay juicy.