One can certainly lose fat and build muscle but there are specific circumstances to doing that. Ones which I believe, from the way people are talking and the reason they're here, would apply to the majority of people here.
This somewhat of a deep dive into the topic but those special circumstances are covered in the first few minutes.
On the subject of resistance training. It's a must imo, not just for GLP1 users, for everyone who wants a long healthy life.
No need for special supplements, eat enough protein 0.6-1g/lb, 0.3g fat per lb, the rest carbs eaten before you train. Start with walking if that's where you are at, add bands, then body weight, then dumbbells or kettlebells, trian 1-2 reps to failure, push a set every so often to failure. Once you feel like you've made some progress then look at getting more serious about resistance training. There are so many various ways to train and implements one can use, it's almost limitless, don't sweat the details, just find what you enjoy and benefit from.