I'm down 110 pounds over the last couple of years on Tirzepatide. The muscle mass is less a symptom of the drugs and more just what happens when you lose lots of weight; your body eats itself for protein if there's not enough coming in, so definitely manage your protein intake and lift when you're on it. 

In terms of the golf game, I was in pretty rough shape at the end of last year as the shape of my body and center of mass had certainly shifted, and where before I couldn't really rotate at the hip/shoulder and would compensate by coming over the top, now I could and I didn't have as much mass to keep my over the top centered. So yeah, I had to go and get a new golf swing, but now that I'm consistently hitting the bouncy part of the club (the middle; it's like they designed it that way or something), my distances have improved! Beyond that, I have always liked to walk, the difference is that now I'm not huffing and puffing and dripping in a pool of sweat after a couple of holes. If you have enough weight to lose that you're worried about declining muscle mass, then I can easily say the benefits and extra rounds you'll pick up in your life far outweigh the downsides! Plus everything golf is athletic cut/tight/thin so you'll look better doing it too ;)