While you are prepping the soup, cook the pasta according to the package directions, Drain and set aside until the end.
Fry the ground beef and onions together in the metal cooking pot in your Instant Pot using the "saute" function on your Instant Pot until the ground beef is cooked and the onions are translucent. Add in the garlic and fry until brown. Drain the fat.
I pre-cook my macaroni so that it doesn't add starch to the soup, which some pasta's can do. If you want to cook it in the Instant Pot, you would have to add it after you release the pressure and then pressure cook it again for 5 minutes. ( which I have done and it works well, but I prefer to pre-make the pasta.)