>Losing weight without losing muscle mass is very hard.

I was with you up to here. In my experience it's easy to maintain a huge proportion of your lean tissue during a weight loss diet: Do some resistance training, get some protein, and don't lose weight too quickly.

There's no need to go to the extreme of a PSMF - which will still have you lose a bunch of muscle on account of being too big a deficit. If you can keep your calories reasonable while on a GLP1 agonist, there doesn't seem to be any reason you'll lose an exaggerated amount of muscle.