Set a 6-qt Instant Pot® to the high saute setting. Melt 2 tbl butter; add garlic and onion, and cook, stirring often, until onions have become translucent, about 3-4 minutes.
Add mushrooms and cook, stirring occasionally, until tender, about 3-4 minutes; season with salt and pepper, to taste.
Stir in chicken broth, rice and thyme. Select manual setting; adjust pressure to high, and set time for 6 minutes. When finished cooking, quick-release pressure according to manufacturer’s directions.
Stir in spinach and remaining 2 tbl butter until the spinach has wilted, about 2 minutes. Stir in peas and Parmesan until heated through, about 30 seconds to 1 minute.