Lightly pat the beef cubes dry with a clean paper towel then toss in the flour, coating each cube. Dust off the excess and season with salt and freshly ground pepper.
With the Instant Pot in Sear mode on high, heat the oil in the insert. When the oil is hot, sear the beef cubes on all sides until deeply golden. Remove and set aside.
If the pot is dry, add a bit of oil, then add the ginger slices, shallot, garlic, and lemongrass and cook, stirring, until the shallot and garlic are soft, but not brown, about 1-2 minutes. Stir in the tomato paste and beef stock. Add the beef back in as well as the star anise, fennel, cloves, bay leaf, and cinnamon stick. It helps if you put the spices in a cheese cloth or large tea bag for easy removal later.
Put the lid on, set the pressure to high and cook time to 35 minutes. Quick release the pressure when cooking time is completed. Give the stew a stir, then add in the potatoes and carrots and cook on high pressure for 7 minutes. Quick release and then stir in the sugar and fish sauce, adjusting for taste. Enjoy!