Add the vegetable broth, soy sauce, rice vinegar, chili sauce, ginger, and black pepper to the Instant Pot. Cook on High Pressure for 2 minutes.
When the Instant Pot is done, carefully release the steam valve, then remove the lid.
Add the vegetables and tofu. Place the lid back on the Instant Pot and cook on high pressure for 3 minutes.
Mix the cornstarch and water in a small bowl to form a smooth slurry.
When the Instant Pot is done cooking, again, carefully release the steam valve and remove the lid. Pour in the cornstarch slurry and stir it in the soup.
Replace the Instant Pot lid and cook on the Sauté setting for 1 minute.
Open the steam handle, remove the lid and stir the soup. Taste the soup and adjust the flavorings if desired.
How to make soup on the stove
Add the vegetable broth, soy sauce, rice vinegar, chili sauce, ginger, and black pepper to a large soup pot on medium-high heat.
When the broth starts to boil, lower the heat to simmer. Cover and simmer for 20 minutes.
Add the vegetables and tofu, cover the soup, and simmer for 15 minutes.
Mix in the slurry and cook for another 5 minutes.