Turn on your Instant Pot and set it to the sauté setting until panel display the word "Hot". Add the vegetable oil to cover the bottom of the inner pot.
Add garlic and ginger and toast until frgrant.
Add Chu Hou paste and toast it for 15 seconds.
Add the beef (and mushroom if using), mix everything to combine.
Pour in water, soy sauce, oyster sauce, rock sugar, and Chinese cooking wine. Stir well.
Close the lid of the Instant Pot and set it to manual high pressure for 45 minutes.
Once it's done, let the pressure release naturally for 15 minutes. Then, carefully quick release any remaining pressure.
Open the lid and give the stew a good stir. Taste and adjust the seasoning if necessary.
If using beancurd tofu sticks, carrots and/or potatos, add to pot now and set to manual high pressure to cook an additional 5 minutes. Quick release when done.