Combine salt, pepper, cumin, and chili powder in a small bowl. Rub all over the beef. (For best flavor, this can be done ahead, up to overnight, but it’s not necessary.)
Set Instant Pot to sauté. Add cooking oil and sear beef all over until browned, about 3–4 minutes per side. Remove the beef and set aside.
Add the unsalted butter and the onion. Stir, scraping up the brown bits at the bottom of the pot, until the onions are translucent, about 5 minutes.
Put the beef back in, and add Shiner, jalapeños or vinegar, fish sauce, bay leaf, and oregano. Close the lid. Set to cook at high pressure for 40 minutes.
Let the pressure come down for 15 minutes on its own before releasing the pressure manually. Remove the lid and set the beef aside in a dish to rest. Cover with foil.
Use a ladle to skim the fat off the top of the liquid that remains. If you have a fat separator, use that, but you should be able to get most of it with a ladle.
Set the Instant Pot to sauté. Add the sweet potatoes and cook about 10 minutes, or until soft.
While the sweet potatoes are cooking, mash the softened butter and flour together with a fork to form a paste. About 3 minutes before the sweet potatoes are done, add the paste to the pot to thicken the gravy.
Using two forks, pull the beef into large chunks—you’re not looking to shred it, just pull it into serving-sized pieces. Serve with the gravy and sweet potatoes.