Huh? Propane is quite easy to deal with, though? Besides being flammable, but that merely means you have to ensure it gets sufficiently diluted in case it feeds indoors, doesn't have an opportunity to asphyxiate occupants, and isn't eager to burn the house down in a typical catastrophic malfunction.

Unlike fluorocarbons, you don't need to worry about leaks beyond the flammability/asphyxiation aspects, and could conceivably flare excess/contaminated charge off (just to prevent an explosive food from being able to form), with no environmental worries beyond the burning/flaring of fossil fuel (and whatever contamination the oil contributes). Might not be legal in a particular jurisdiction, but I assume that's a product of fluorocarbons being the norm and them being an environmental issue to leak, supporting a blanket ban on leaking any.

The CO2 heatpump needs more than 150 bar, like having a small OceanGate in your attic.