Optimal for muscle growth? No. You’ll want to increase the protein by a minimum of 10% to start getting into optimal amounts. A 40/30/30 of C F P is seen as a “balanced” diet most of the time. High protein (around 40% with carbs going to 30%) or VERY high protein (protein at 50%) is what you’ll see many bodybuilder types follow during normal training. 20% protein will not be close to optimal for muscle growth.