Here in the mid-Atlantic, my air-air heat pump struggles once things get well below freezing. Which it does a few days a year.

On those days, there's a backup resistance heater. Which is vastly more expensive, but since it's only run on occasion, it wouldn't be worth it install a geothermal heat pump.

I would love to, but the additional cost is tens of thousands of dollars. The since the alternative costs perhaps a couple of hundred dollars per year, the time to breakeven is many decades.

It's still quite clear that a heat pump is a very good all-electric option, especially since it provides cooling in the summer. Which is absolutely mandatory around here, and will get more and more so over the years. Which, ironically, will also reduce the use of the resistance heater from "very rare" to "practically never".