I went from 118kg to 79 in 4 months - Dr. Berg's Healthy Keto

By following Dr. Berg and going into keytosis and intermittant fasting I went from 118kg to 79 in 4 months. Many of my freinds including a medical nurse were so concerned I was going to become sick I had a private 40 page medical report done. I was geen flagged on every health marker. Whereas previously I had been limping on swollen legs and feet for some 8 years, sometimes could not put a boot on my right foot. All these conditions including high blood prressure went away. I was 63 then and my metabloic rate was equated to that of a fit healthy 43 year old, my lung age at 47. This was late August 2017. In 2019 I decided my fat was stable at 12% body weight and joined a gym for the first time in my life. 7 weeks later I become 3rd in Ireland in the CrossFit Open. At 64 in a CrossFit box of 200 acheived 21st in the box. The 20 above me average 33.5 years. I am just so increadibly fit and have great endurance. My problem at the moment is in spite of trying every tweak I can find, suppliments, workouts, and diet, I fail to gain muscule. Still looking for the answers.