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. Set a pressure safe 7-inch round baking dish in the cooker. (A springform pan will leak and should not be used.) Stack the fillets in the dish, sprinkling each with an even coating of the spice mixture (about 1/2 teaspoon on each). Set the stick of butter on top of the fillets and lock the lid onto the pot.
Option 1 Max Pressure Cooker
Press Pressure cook on Max pressure for 7 minutes with the Keep Warm setting off.
Option 2 All Pressure Cookers
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.