Preheat your oven to 300 degrees F. Set a silicone bundt pan on a large baking sheet pan and set aside.
Place your egg whites, warm water, vinegar, berry extract and berry liquid stevia in a stand mixer and whip until stiff peaks form.
Place your egg white protein powder, whey protein powder, water, confectioners, Allulose and salt in a high powered blender and blend until smooth.
Once your egg whites are stiff, slowly pour your blender mixture into the stand mixer on low speed to incorporate.
The whites may flatten a little but don't worry, this will not matter and the cake will still rise. Once combined, pour batter into the ungreased silicone bundt pan. Bake for 1 hour. Don't open oven door, turn oven off and allow cake to stay in oven for another 5 minutes. Remove and allow to cool in bundt pan on counter for 2 hours. After that, flip cake over onto baking sheet pan for another hour.
Carefully take a sharp knife to loosen cake around the center tube. You should now be able to carefully remove the cake from the pan.