Select the “Sauté” function and the “high” setting on the Instant Pot®. Add olive oil and one tablespoon butter. Add onions and half the garlic powder. Season with salt and black pepper, to taste, and stir to combine. Cook, stirring occasionally, until the onions soften, approximately 4-5 minutes.
Add mushrooms and season with remaining garlic powder, and additional salt and black pepper, if desired. Sauté, stirring occasionally, until the mushrooms are golden brown and start to release their liquids, approximately 5 minutes.
Add the Marsala wine and thyme. Cook, stirring occasionally, until the wine is reduced by half and the strong aroma dissipates, approximately 4-5 minutes. Transfer sautéed mushrooms and onions to a bowl and set aside.
Add another tablespoon of butter and one-quarter cup chicken broth to the Instant Pot®. Gently scrape up any browned bits off the bottom with a wooden spoon.
Add the rice and toast, stirring occasionally, for 1-2 minutes.
Add the remaining broth and stir to combine. Cover and lock lid into place. Set valve to “Sealing” and select the “Manual” and “High Pressure” settings. Adjust cook time to 22 minutes.
Once cook time is complete, allow pressure to release naturally for 10 minutes, then do a quick release for any remaining pressure.
Carefully remove the lid and fluff the rice with a fork. Add the mushroom mixture and the remaining butter to the Instant Pot®. Add the green onion and parsley and stir to combine.
Turn off the Instant Pot® and transfer the rice to a serving dish. Serve immediately with your choice of entrees. Enjoy!