Preheat the oven to 180C/350F and grease a Bundt pan very generously with oil, making sure all grooves are coated.
Whisk the almond flour, whey protein isolate, erythritol, stevia powder, lemon zest, baking powder, and baking soda in a large bowl until evenly combined.
Toss the blueberries with the coconut flour in a separate bowl until coated.
Fold the coated blueberries into the dry ingredients until evenly distributed.
Whisk the eggs, almond milk, melted refined coconut oil, and lemon juice in another bowl until smooth.
Pour the wet mixture into the dry mixture and stir until fully combined, scraping the sides and bottom of the bowl to ensure no dry pockets remain.
Pour the batter into the prepared Bundt pan, smooth the top, and tap the pan gently on the counter to settle the batter.
Bake for 40 minutes, or until a toothpick inserted into the thickest part comes out clean or with a few moist crumbs.
Cool the cake completely in the pan before removing it from the mold. Chill the cooled cake for about 1 hour before slicing and serving.