Put potatoes in the bottom of the instant pot with 1 c water and 2 tbsp butter, a pinch of salt and pepper. Place the pots steam rack over the potatoes.
Rub the sides of the salmon fillets with the paprika and lemon zest. Put skin side salmon on the rack. Put on the lid, making sure the steam valve is in the sealing position and set the pressure cooker to high pressure 3 minutes. Carefully turn the steam value to the venting position to release the pressure.
Remove salmon and rack and set the cooker to saute to normal heat. When the potatoes start sizzling and cook, stirring until softened. 1-2 minutes and season salt and pepper. Smash potatoes with fork until chunky.
Turn off cooker, add the spinach to potatoes until wilted. 1-2 minutes. Season and serve salmon with lemon wedge.