My SO got me into the gym this last year.  I had the same goal as you.  5'6" 140 -> 120 and build muscle. At first I put on a lot of muscle, but didn't lose much fat.  Once I had a good base I backed off on the weights and hit cardio hard.  I went from 4 hard weight workouts a week, to doing 2 full body workouts and 2-3 runs/HIIT workouts.  I think I dropped like 8 lbs the first 3 wks after I made the switch, and have been steadily losing weight since then.  u/ThinBlondeBeast gave me some good advice in this post that has been working for me.