In a bowl with a lid that will fit your steak, whisk together the soy sauce, fish sauce, oyster sauce, sesame oil, sugar, garlic, ginger and red pepper flakes. Add the beef and stir until completely coated. Marinate for 30 minutes or up to overnight.
Add all the beef and sauce to the Instant Pot. Cook for 10 minutes on high pressure. Allow pressure to naturally release for 10 minutes then force the rest of the pressure by opening the valve.
Turn the Instant Pot to saute mode. Whisk together the cornstarch and water in a small bowl. Add the cornstarch slurry to the Instant Pot once it's boiling. Stir until thickened. Serve over rice.