> For the people who lift weights while on this/these drugs, how much lean muscle do they lose?

I was 92kg when I started on liraglutide (I was doing GLP-1 agonists before it was cool!) and 67% of muscle mass (61kg). I'm now at 69kg and 82% of muscle mass (56kg). I'm doing weight and resistance training twice a week, in addition to aerobic training.

One nice thing, while muscles don't become more massive, they for sure become more pronounced and visible with weight loss.