Cut off the stems of the collard greens, removing any part of the central stem that seems tough. Stack 2 or 3 leaves on top of each other, roll them up so that they form a long tube, and cut them into thin strands:
Repeat with all the collards.
Heat the pressure cooker (use the Sauté button on the Instant Pot). Add the onions and 2 tablespoons water and cook, stirring, until the water evaporates. Keep cooking and stirring until the onions start to brown. Add the garlic and red pepper flakes, and cook for 1 more minute.
Stir in the collard greens, add the 1 cup of water, and seal the cooker. Bring to high pressure (use the Manual button on the Instant Pot) and cook at high pressure for 3 minutes. (If you are using small, baby collards, cook at high pressure for only 1 minute.) Remove from heat and use a quick-release method to reduce the pressure. Check the collards for tenderness; if they’re still tough, put them back on the heat, but don’t seal the cooker. Cook until tender. Salt, if desired, with smoked salt and serve (using a slotted spoon) with additional red pepper flakes.