If using dried shiitake mushrooms: Place mushrooms in a medium bowl and cover with hot water for 30 minutes. Drain liquid and thinly slice.
Add to the Instant Pot: mushrooms, tofu, bamboo shoots, garlic, Asian sweet chili sauce, garlic, ginger, white pepper, sugar, rice vinegar, soy sauce, garlic chili paste, and vegetable stock.
Lock on Lid and point Pressure Valve to Sealed.
Cook at High Pressure for 5 minutes. When the Instant Pot beeps, do a 10-minute Natural Pressure Release and then manually release the rest of the pressure.
Select the Sauté mode. Add a few drops of oil to the beaten egg and whisk to combine.
When the soup begins to bubble, pour the beaten eggs into the middle of the cooking pot. Wait for a few seconds and then stir the egg mixture in a circular motion slowly a couple of times.
If you want the soup to be thicker, mix cornstarch and water in a small bowl until fully combined. Add the mixture to the pot and gently stir, let it simmer for 1-2 minutes. If you want the soup even thicker, add another of 1 tablespoon of cornstarch mixed with water. The soup will also thicken slightly after it cools off thanks to the cornstarch mixture.
Turn off the Instant Pot. Add the spinach to the pot and stir to combine. Add 1/2 the sliced scallions and stir.
For extra sour flavor, add one more tablespoon of vinegar at the end.
Serve garnished with scallions.