Mix the paprika, onion powder, salt, and pepper in a small bowl until uniform
Pour the water into an Instant Pot. Set the pot’s rack (with the handles up) or a pressure-safe trivet inside the pot. Use aluminum foil as baking dish in the cooker. Stack the fillets in the dish, sprinkling each with an even coating of the spice mixture (about 1/2 teaspoon on each). Set the butter on top of the fillets and lock the lid onto the pot.
Pressure cook or Manual on High pressure for 8 minutes with the Keep Warm setting off.
Use the quick-release method to bring the pot’s pressure back to normal. Unlatch the lid and open the cooker. Use silicone cooking mitts or thick hot pads to transfer the baking dish to a heat-safe work surface. Use a metal spatula to transfer the fillets one by one to serving plates or a platter. Spoon some (or all) of the buttery “sauce” in the baking dish over the fish