At a body weight of 84kg, what will serve you best is increasing your calorie intake, mainly protein and a few carbs.
You said you can't grow anymore and you're as young as you are? You need to eat more food, plain and simple. At least 300 grams of protein every day at your body weight consistently, and as you gain size, your protein intake needs to increase more.
At 235 lbs fairly lean right now, I have to get in at least 400 grams of protein daily or I will not grow.
You can grow. Eat more food. Not shitty supplement powders to fill in 150 grams of protein. Meat, eggs and milk.
And be lifting to failure in the gym, no matter which rep range you choose. Do max reps every set. Push beyond your limits without injuring yourself. Give your body a reason it needs to be bigger and stronger.
With a sarms stack and increased protein intake, you should easily gain 10lbs.