Grease a 6-inch heat-proof baking dish or springform pan with coconut oil, and line the bottom with parchment paper. If using a springform pan, wrap a sheet of foil around the bottom to prevent the cake batter from leaking out, and water from leaking in. Place a steamer rack or trivet in the Instant Pot bowl, and add 1½ cups water.
In a medium bowl, mix the almond flour, cacao powder, baking soda, salt, and monk fruit powder until combined. Set aside.
In another medium bowl, beat the eggs and stir in the coconut milk, coconut oil, and vanilla. Add the dry ingredients and mix just until combined (the batter will be thick, like brownie batter.)
Pour the mixture into the prepared cake pan, cover the top with foil, and place it on top of the rack in the Instant Pot.
Secure the lid and move the vent knob to the sealed position.
Select “Manual” and cook on high pressure for 40 minutes. Once the cooking time is up, let the steam release naturally for 10 minutes then carefully move the vent knob to “Venting” to release the rest of the pressure.
Lift the cake from the Instant Pot, remove the foil covering the top, and cool on a rack for 10–15 minutes before serving.