Combine the almond flour, coconut flour, flaxseed meal, cocoa powder, and sweetener together in a large bowl. Sift to ensure there are no clumps.
Mix in the remaining cake ingredients. Start with two eggs, and if the batter is still dry add a third egg.
Grease a round cake pan that fits inside the Instant Pot. Pour the batter into pan and spread the batter so that it is even. Cover the top of the pan with a paper towel and aluminium foil to prevent liquid from pooling at the top of the cake.
Add a cup of water and a trivet to the bottom of the Instant Pot. Then lower the cake into the Instant Pot to rest of the trivet. Close the lid and turn the pressure valve to seal.
Cook the cake for 35 minutes using the "manual", "pressure cook", or "cake" function on your Instant Pot. Let the pressure release naturally for at least 10 minutes before doing a quick release.
Remove the cake from the Instant Pot and let it cool completely before frosting/icing.
Mix the frosting/icing ingredients together in a bowl. Store it in the refrigerator until the cake is ready to frost/ice. Frost/ice the cake and enjoy!