Turn on the Instant Pot and select Sauté function. Add butter and olive oil; stir until the butter melts, about 2 minutes. Add mushrooms and cook for 3 minutes, stirring occasionally. Add chopped onion and cook for 2 more minutes. Add rosemary sprig and cook for 1 minute.

Stir rice into the pot until each grain is coated with the butter and olive oil mixture, about 2 minutes. Pour in the white wine and simmer for 3 minutes.

Pour in stock and stir, scraping the sides of the pot. Simmer for 1 minute.

Close and lock the lid. Turn the venting knob to sealing. Select high pressure and set a timer for 6 minutes. Wait for the pressure to build.

Release pressure carefully by tapping the venting knob with a wooden spoon. Stand back and turn the knob to vent. Remove the lid after pressure is fully released, approximately 5 minutes.