Place the dried guajillo and ancho chiles in a bowl and cover with boiling water. Let them soak for 15 minutes until softened. Drain, reserving 1/2 cup of the soaking liquid.
Add the softened chiles, reserved soaking liquid, fire-roasted diced tomatoes, quartered onion, garlic cloves, oregano, and cumin to a blender. Blend until completely smooth.
Season the pork shoulder chunks with salt and black pepper. Set the Instant Pot to saute mode, add a drizzle of oil, and sear the pork in batches until browned on all sides, about 3 minutes per batch.
Pour in the blended chile sauce and chicken broth. Stir to combine and scrape up any browned bits from the bottom of the pot.
Lock the lid, set the valve to sealing, and cook on high pressure for 35 minutes. Allow a natural pressure release for 15 minutes, then quick release the remaining pressure.
Open the lid and use two forks to shred the pork right in the pot. Stir in the drained hominy. Set the pot to saute mode and simmer for 5 minutes to let the hominy warm through and the flavors meld. Taste and adjust salt as needed.
Ladle the pozole into deep bowls and serve with shredded cabbage, sliced radishes, diced avocado, fresh cilantro, lime wedges, and tortilla chips.