The short of it is that Metformin does seem to induce good metabolic changes but it also reduces the physiological response to exercise which is also great for your metabolism, function, mental health, etc.
I know a few folks who were on metformin long term for diabetes related things, and after the switch, lost a TON of weight from metabolic changes in just that year compared the entire past.
As with both generally, they're starting to clamp down on prescribing/filling for non-diabetic folks (aka, people using it just for weight and not clinical diabetes itself).
The advantage here is that this is not ‘off label’ at all for many people today.
"...Mounjaro can be used on its own in patients who cannot take metformin (another diabetes medicine)..."