Turn on a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Add oil and onion. Cook, stirring often, until translucent, 3 to 5 minutes. Add a splash of water to stop cooking.
Add 8 cups water, cabbage, beets, potatoes, carrots, bell pepper, bay leaves, salt, and pepper to the pot. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 40 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid.
