In a small bowl, whisk together oregano, brown sugar, salt, chili powder, cumin, and garlic powder. Rub spice mix all over chuck roast.
Set Instant Pot to Sauté and add oil. Sear all sides of chuck roast until golden, about 2 minutes per side. Pour in lager then scatter onions over chuck roast and secure lid.
Set Instant Pot to Pressure Cook/Manual on High for 55 minutes. Let pressure release naturally for 10 minutes, then follow manufacturer’s guide for quick release, making sure to wait until the cycle is complete before unlocking and removing the lid.
Preheat oven to 375°F and line a large baking sheet with aluminum foil.
Remove roast and use two forks to shred into bite-size pieces.
Spread an even layer of chips onto the baking sheet, then top with one-third of the cheese, jalapeños, and shredded beef. Repeat twice more. Bake until cheese is melty, about 10 minutes.
Garnish with avocado, radishes, cilantro, and red onion. Serve with lime wedges.