Turn the instant pot to Sauté on high. Brown the short ribs in the pot on all sides. Cancel saute setting, then add remaining ingredients. Toss mushrooms on top. Place cover on instant pot and set steam valve to sealed.
Push the pressure cook/manual button and set timer to 50 minutes. When cook time is over, let machine naturally vent for 10-15 minutes before turning steam release valve to venting to release the rest of the pressure. Serve ribs over rice, spooning the liquid over the top.