Turn Instant Pot on to the Saute (High) setting. Wait 5 minutes to allow the temperature to get high.
Add coconut oil and let it melt. Tilt the Instant Pot to swirl around coconut oil to cover the bottom of the pan. Make sure the oil is sizzling hot (put a drop a water to check that it sizzles). NOTE: If you skip this step, the popcorn will stick to the bottom and burn.
Add popcorn kernels and use a spatula to coat the popcorn well. Stir for about 30 seconds. Cover with a clear Instant Pot lid.
It will take about 2 minutes for the popcorn to start popping. Do NOT take off the lid. Use the lid to see when most of the popcorn is popped (about 3/4 done or about 3-4 minutes), and then turn it off (letting the rest of the kernels pop for another 30 seconds or so).
Remove the lid and then take out the inner pot. Pour the popcorn into a large bowl and let it sit for about 2-3 minutes to let the coconut oil set in. This adds to the flavor.
Add butter (optional) and salt to taste.