In a large mixing bowl, whisk together the dry ingredients: flour, cornmeal, sugar, baking powder, and salt.
In a medium bowl, whisk the wet ingredients: egg, milk, and avocado oil. Pour the liquid mixture into the dry ingredients and stir until just combined.
Gently fold in the fresh blueberries (toss with a little flour first if using frozen).
Spray silicone molds with non-stick cooking spray. Fill each cavity 3/4 full with muffin batter.
Place a trivet or silicone sling in the Instant Pot. Add 1 cup of water to the bottom.
Cover one filled egg mold with aluminum foil or mason jar lids, stack the second mold on top.
Close the lid, seal the vent, and cook on high pressure for 8 minutes. Allow a natural release for 2–3 minutes, then release the remaining pressure.
Remove molds carefully and place on a wire rack. Let cool before removing muffins from the molds.
