Add vegetable oil to the Instant Pot and set it to sauté.
Add the ground beef and onion. Cook and crumble until the beef is almost cooked through, about 5 minutes.
Add the garlic, Worcestershire sauce, tomato paste, salt, and pepper, then cook for 2 more minutes.
Pour in 1/4 cup of the beef broth and scrape the bottom of the pot to release any stuck pieces.
Add the remaining broth and the dry elbow macaroni. Stir so the pasta is submerged as evenly as possible.
Lock the lid, seal the valve, and set the pressure cooking time to 5 minutes.
When the cooking cycle is complete, quick-release the steam. Open the lid carefully and stir in the shredded cheddar until it is completely melted and combined.
Notes
Optional variation: stir in steamed broccoli after the cheese melts for extra color and crunch.