Use a sharp serrated knife to cut off the stem of each artichoke. Then cut about ½ inch off of the leaves at the top of the artichoke. Use kitchen scissors to trim off the pointy ends of the outer leaves.
Rinse artichokes under cold water and then place them in a bowl of cold water for 5 minutes to soak.
Add 1 cup of cool water to the Instant Pot inner pot (use 1 ½ cups of water for an 8 quart pot). Cut the lemon in half. Cut one half of the lemon into 2 or 3 slices (reserve the other half of the lemon), and place the lemon slices in the water in the Instant Pot.
Put the metal trivet in the Instant Pot. Drain the artichokes and place them, stem side down, on top of the trivet. Squeeze the juice from the reserved half of the lemon over the artichokes.
Close the Instant Pot lid and turn the steam release valve to the sealing position. Pressure cook on high pressure for 15 minutes for small artichokes (about 200 grams each), 20 minutes for medium artichokes (about 300 grams each) or 25 minutes for large artichokes (about 400 grams each). The Instant Pot will take about 10 minutes to reach pressure and then the cook time will begin counting down.
When the cook time ends, immediately quick release the pressure by carefully turning the steam release valve to the venting position using the handle of a long spoon. When the pin drops down, carefully open the Instant Pot lid. Use tongs to remove the artichokes from the pot and let them cool slightly before serving.
Serve artichokes with melted butter and an extra squeeze of lemon juice, or with your desired dip.