Set Instant Pot to Sauté. Add a little oil or butter and cook the onion 2–3 minutes until softened. Add garlic and mushrooms; cook until the mushrooms are browned, about 4–5 minutes.
Stir in the rinsed quinoa, broth, thyme, and soy sauce. Season with a pinch of salt and pepper. Make sure nothing is stuck to the bottom.
Lock the lid, set to High Pressure for 1 minute. When it finishes, let it naturally release for 10 minutes, then quick-release any remaining pressure.
Fluff with a fork and stir in the butter. Taste and adjust seasoning.