Using highest sauté function, heat oil in Instant Pot until shimmering.
Add garlic and ginger and cook, stirring frequently, until fragrant, about 30 seconds.
Stir in broth, water, sake, and soy sauce, then stir in beef and mushrooms.
Lock lid into place and close pressure-release valve.
Select high pressure-cook function and cook for 25 minutes.
Turn off Instant Pot and quick-release pressure.
Carefully remove lid, allowing steam to escape away from you.
Nestle noodles in even layer into pot (you may need to break noodles to fit).
Partially cover pot and cook, using highest sauté function, until noodles have softened on bottom, about 3 minutes.
Uncover pot, flip noodles, and stir to separate.
Stir in bok choy and cook, tossing occasionally, until noodles and bok choy are tender and broth has thickened slightly, about 2 minutes.
Season with extra soy sauce to taste.
Divide noodles evenly among serving bowls and sprinkle with scallions.
Serve, passing shichimi togarashi separately.
