As Heat Pumps Go Mainstream, a Big Question: Can They Handle Real Cold? - The New York Times

While heat pumps do become less efficient in subzero temperatures, many models still operate close to normally in temperatures down to minus 13 degrees Fahrenheit, or minus 24 Celsius. Some of the latest models are even more efficient, and many "cold" countries, like Norway, Sweden and Finland, are increasingly embracing heat pumps..

https://www.nytimes.com/interactive/2023/02/22/climate/heat-pumps-extreme-cold.html