alt Hacker News> Studies suggest muscle loss with these medications (as indicated by decreases in fat-free mass [FFM]) ranges from 25% to 39% of the total weight lost over 36–72 weeks. This substantial muscle loss can be largely attributed to the magnitude of weight loss, rather than by an independent effect of GLP-1 receptor agonists, although this hypothesis must be tested. By comparison, non-pharmacological caloric restriction studies with smaller magnitudes of weight loss result in 10–30% FFM losses
Emphasis my own. In short: no evidence this is anything other than due to rapid weight-loss.
The part highlighted by you was just an optimistic supposition made at the time when the first article has been published. That supposition only expressed wishful thinking that was not based on any data.
The study on mice published in the second article has been made specifically to test this optimistic supposition and the results have shown that it had been false, i.e. the weight loss caused by semaglutide is different from the weight loss caused only by calorie restriction.
More studies are needed to elucidate whether this effect of semaglutide is really harmful or maybe it can be reversed or avoided by combining the medication with a better diet, e.g. with a higher protein intake.