Heavily season both sides of the roast(s) with salt and pepper. Heat Instant Pot with "Sauté" button. Add 1 Tbsp of oil. Sear both sides of one roast. Set aside. Repeat with second roast. Remove from Instant Pot and set aside.
Add beef broth to Instant Pot to de-glaze the bottom of the pot. Return roasts to pot. Cancel the "Sauté" button and cook on "Meat/Stew" or "Manual" (high pressure) for 120 minutes.
Let cook. Once finished, turn the vent/quick release valve to the open position until you no longer hear or see steam, and the float valve is down.
Open lid. Scoop the meat out of the instant pot and shred with two forks, discarding any pieces of fat. Drain the broth with a fine mesh sieve. Skim the fat off the top and add 1 cup (+) of the juices back into the shredded beef. (Just enough for it to seem moist.)
Heat Instant Pot with "Sauté" button and melt the shortening/coconut oil. Add diced onions and cook for 5 minutes or until soft and translucent.
Add flour and stir with the onions for 1 minute. Add the green chiles, salsa verde, garlic powder, salt, and cumin. Cook until thick. Add meat mixture into the onion mixture and heat thoroughly.
Fill tortillas with 1/3 to 1/2 cup meat each and fold burrito style.
Heat 2 cups of oil in a large pot. Place chimichangas carefully seam side down into the oil and fry both sides until golden brown (approximately 45 seconds each side.) Allow to drain on a paper towel lined plate.
Serve with sour cream, salsa, guacamole, cheese or other desired toppings.