Combine the seasonings (salt, pepper, onion powder, garlic powder, Italian seasoning) in a plate or shallow bowl.
Meanwhile, set the instant pot to “saute” to let it warm up. Roll the roast in the seasonings so that most of the outside of the roast is coated.
Add some oil to the pot and add the roast. Sear each side for 30-60 seconds each.
Remove the roast and add the cut-up white onion and butter. While you sauté the onions, work to deglaze the pan and scrape up those bits of flavor from the bottom.
When the onion is mostly done, add the balsamic vinegar and Worcestershire sauce. Then add 2 cups of beef broth. insert a trivet to the bottom of the pan, and add the roast on top of the trivet.
Note: cooking the onions along with the beef will make the onions cook down almost to mush. Another option is to remove the onions and set them aside to go back in with the carrots and potatoes.
Put the lid on the instant pot and set it to the “meat/stew” setting. Cook for 70 minutes in this setting. (If using a frozen roast or a considerably larger roast, you can cook for 90 minutes, skip the searing step if you are using a frozen roast.)
Do a natural pressure release (NPR) for at least 20 minutes, then open the lid, add some carrots and potatoes, close the lid and cook for another 8-10 minutes on the manual/high-pressure setting.
When done do a 10 minute NPR.
Remove the vegetables and meat from the pot, and add a cornstarch slurry of 1/4 cup cold water mixed with 3-4 Tablespoons of cornstarch.
Season with salt and pepper to taste. Cook on the sauté setting until the gravy is thickened. Serve the meat, vegetables, and gravy altogether.