Pour 1 ½ cups water in the Instant Pot inner pot. Add a steamer basket to the pot. (If you don't have a steamer basket, you can set the potato pieces on the metal trivet that came with the Instant Pot.) Put the potato pieces in the steamer basket and set the eggs on top of the potatoes.
Close the Instant Pot lid and turn the steam release valve to the sealing position. Pressure cook at high pressure for 4 minutes. The Instant Pot will take about 15 minutes to reach pressure and then the cook time will begin counting down.
As soon as the cook time ends, quick release the pressure by turning the steam release valve to the venting position using the handle of a long spoon. As soon as the steam escapes and the pin drops down, open the Instant Pot lid.
Immediately put the eggs in a bowl of ice water. Carefully transfer the potatoes to a large plate or baking sheet, in a single layer, and allow them to cool.
While the potatoes cool, chop the celery and onion. Then mix up the dressing: whisk together the mayonnaise, pickle relish, apple cider vinegar, mustard, salt and pepper in a medium bowl. Chill the dressing in the refrigerator until the potatoes have cooled completely.
Peel and chop the hard boiled eggs. Place the cooled potatoes in a large bowl. Add the chopped eggs, celery, onion and dressing to the bowl. Stir until combined. Taste and add more salt and pepper as needed. Chill potato salad in the refrigerator for at least 2 hours before serving.