Arrange beef bones on a paper towel-lined plate and microwave in batches until well-browned, 8 to 10 minutes. Add bones and 6 onion quarters to the pressure cooker.
Add 2 quarts water, fish sauce, ginger, cinnamon stick, star anise, cloves, sugar, salt, peppercorns, and steak trimmings to the pot. Lock lid and select high pressure. Cook for 1 1/2 hours. Allow the pressure to release naturally for 15 minutes, then quick-release any remaining pressure.
Strain broth through a fine-mesh strainer lined with cheesecloth. Discard solids. Skim excess fat from the surface of the broth and let it settle for 5 minutes. (Broth can be refrigerated for up to 4 days or frozen for up to 1 month.)
Slice steak crosswise into 1 1/2-inch-wide strips and freeze on a large plate until very firm, 35 to 45 minutes. Once firm, shave beef against the grain as thin as possible using a sharp knife. Refrigerate slices until ready to serve.
Add 1 quart of water to the strained broth in the cleaned pressure cooker. Bring to a boil using the sauté or browning function. Season broth with salt to taste. Add noodles and let cook, stirring occasionally, until soft and pliable but not fully tender.
Divide noodles among serving bowls. Arrange steak slices over the noodles and top with thinly sliced onion. Ladle hot broth into each bowl, ensuring the steak cooks through. Serve with bean sprouts, herbs, lime wedges, sriracha, hoisin, and extra fish sauce.