Set the Instant Pot to Sauté on Normal/Medium. Let it heat for 5 minutes.
Once the Instant Pot is heated, add all three broths (beef, chicken, and vegetable) to the pot. Stir in half of the chopped onion and all of the chopped scallions. Season with salt, pepper, and a pinch of Old Bay seasoning to taste. Bring to a simmer for 10 minutes to allow the flavors to meld.
Add the corn and sliced lotus root into the broth. Continue to simmer for an additional 5 minutes.
While the broth simmers, arrange the Udon noodles, ramen noodles, mushrooms, bok choy, shrimp, pork shabu, beef brisket, fish balls, and dumplings on a platter or in bowls for easy access. You can also drizzle a little chili oil over the ingredients for extra flavor.
Once the broth is ready, set the Instant Pot to Pressure Cook on High for 5 minutes. After the cooking time is complete, allow for a 5-minute natural pressure release, then carefully quick-release the remaining pressure.
Once the pressure is released, transfer the Instant Pot to a trivet or keep it on the Keep Warm setting. Serve the hot pot with the cooked broth and allow each person to cook their choice of meats, noodles, and vegetables in the simmering broth. Enjoy!