Select Sauté and let the Instant Pot® heat up for about 2 minutes. Add the bacon, garlic, and mushrooms, and sauté for about 6 minutes, until the bacon starts to brown.
Press Cancel. Add the broth. Using a wooden spoon, scrape up any browned bits stuck to the bottom of the pot. Add the green beans to the pot.
Lock the lid into place. Select Pressure Cook or Manual. Set the pressure to High and the time to 2 minutes (4 minutes if using frozen green beans). Make sure the steam release knob is in the sealed position. After cooking, quick-release the pressure.
Unlock and remove the lid. Stir in the lemon juice and balsamic vinegar.
Serve immediately, or place the green beans in an airtight container and refrigerate for up to 4 days.