Turn on a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Heat oil. Add beef and cook until browned, about 3 minutes per side. Add onion, taco seasoning, 1/4 cup water, and garlic salt. Stir to combine.
Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 30 minutes. Allow 10 to 15 minutes for pressure to build.
Meanwhile, bring 2 1/2 cups water to a boil in a large saucepan. Add rice and stir for 1 minute. Cover saucepan tightly. Reduce heat to a simmer and cook until rice is tender, 20 to 25 minutes. Remove from heat and let cool completely.
Release pressure naturally according to manufacturer's instructions, 10 to 40 minutes. Let cool completely.
Divide beef and rice among 6 reusable containers. Top with equal amounts of black beans, corn, and Cheddar cheese. Cover and refrigerate.
