Set your Instant Pot to the sauté mode. Add the olive oil, and when hot, place the beef shank in the pot. Brown both sides to a nice golden color, then set aside.
In the remaining oil, add the chopped onion. Sauté until golden and caramelized. If needed, add a bit of water to deglaze the pot.
Introduce the garlic and mushrooms, cooking until they are golden.
Stir in the paprika, curry powder, and salt, ensuring the mushrooms and onions are well coated. Pour in the beef broth and tomato passata, mixing well.
Return the beef shank to the pot, securing it amidst the liquid and veggies. Close the lid, set the Instant Pot to high pressure, and cook for 45 minutes.
When cooked, remove the beef shank, shred it, and return the meat to the pot.
Set the Instant Pot to sauté mode and cook uncovered until the stew thickens to your liking.
Serve hot in deep bowls, topped with fresh pepper and a dollop of sour cream or Greek yogurt, if desired.