Set the Instant Pot to 'Sauté' mode. Add olive oil, and once hot, add the chunks of beef. Sear the meat on all sides for about 5-7 minutes until browned. Remove the beef and set aside.
In the same pot, add chopped onion and sauté for about 3-4 minutes until softened. Add garlic and cook for an additional 1 minute until fragrant.
Return the browned beef to the pot. Stir in lime juice, apple cider vinegar, cumin, oregano, smoked paprika, chili powder, salt, and pepper. Mix well to coat the beef with the spices.
Add beef broth and bay leaves. Close the lid and set the Instant Pot to 'Pressure Cook' on high for 60 minutes. Once the cooking time is complete, allow for a natural release for about 15 minutes before manually releasing any remaining pressure.
Carefully remove the beef from the pot and shred it using two forks. Return it to the pot and mix with the juices to absorb the flavors.
In a separate pan over medium heat, warm the corn tortillas for about 30 seconds on each side until pliable.
Layer the shredded barbacoa beef on the warm tortillas. Top with fresh cilantro and a squeeze of lime juice. Add sliced radishes if desired for an extra crunch.
Notes
Serve the tacos on a wooden board or platter, alongside lime wedges and a small bowl of chopped cilantro for guests to garnish as they like.