Dice the dried mushrooms, add them to a small bowl, and cover them with 1 cup boiling water. Set aside.
Set the Instant Pot to Sauté and heat it. Add the onions, carrots, and celery. Cook the ingredients for about 3 minutes, stirring to prevent them from sticking. Add water a tablespoon at a time if needed.
Mix the fresh mushrooms with the rest of the vegetables and cook them until they soften and release their moisture.
Turn the Instant Pot off. Add the dried mushrooms and their soaking water. Then add the thyme, garlic powder, barley, broth, soy sauce, and bay leaves. Mix all the ingredients using a wooden spoon or non-abrasive utensil to sweep the bottom of the pot.
Place the lid on the Instant Pot and set the steam handle to Sealing. Select High Pressure for 25 minutes and turn off the Warming setting.
After the Instant Pot has finished pressure cooking and the beeper has sounded, leave it alone for 15 minutes (nature pressure release).
Manually open the steam release valve and let the pot de-pressurize. Then, remove the lid.
Stir the soup, then taste the barley to ensure it is tender. Season with additional soy sauce or salt/pepper as desired.