On the Instant Pot, press the “sauté” button. Adjust to the “high” setting and press “start”. (Some Instant Pot models only require you to select "saute") Add two tablespoons of olive oil and allow pot to preheat.
Add the beef into the Instant Pot and season with salt and pepper. Brown all sides of the beef, which will take about 10-15 minutes. Once the beef is browned, carefully remove the inside pot and pour the beef into a colander to discard the excess liquid. Set the cooked beef aside and place the silver pot back into the Instant Pot.
Add the remaining two tablespoons of oil into the pot. Then add onion, carrots, celery, radishes, mushrooms, garlic and thyme, and saute until onions are translucent, about 10 minutes. Next, add the tomato paste and stir to combine.
Pour in the beef broth and scrape any browned bits from the bottom of the pot, add browned beef cubes and stir.
Place the lid on the Instant Pot and turn into place. Press “Pressure Cook” and then select the preset for “Stew”. Confirm the setting of “High” heat and 35 minutes. Switch the valve to “seal” and press “start”. When the stew is finished cooking, release pressure manually by switching the valve to vent, or naturally by waiting about 10-15 minutes.
Carefully remove the cover, stir the stew to incorporate and season with salt and pepper to taste. Serve as is, or over cauliflower mash. Garnish with chopped fresh parsley if desired and enjoy.