Say there’s a hypothetical AC that works very well and requires no environmentally problematic materials and lasts forever,
Does the simple act of moving heat from inside to outside do any measurable, meaningful harm to nature?
Does the simple act of moving heat from inside to outside do any measurable, meaningful harm to nature?
No, the heat moved is trivial compared to the heat coming in from the sun. That said, urban design (concrete, asphalt, etc) that absorbs a lot of extra heat will have a noticeable effect, definitely on a local level. Cities with a lot of green are a few degrees cooler as well, in part because of shade (the heat is captured higher up), in part because of evaporation.
It would still take energy to run. How is/would that energy produced?
For instance, I challenge you to prevent the heat death of the universe.
Certainly better than combustion which creates heat AND creates gasses which trap that and other radiation as heat.