My air sourced heat pump keeps my house warm just fine in the Finnish winter where temperatures of -30C aren’t unheard of. I’m not exactly sure how it works, but I assume there’s coils that’ll produce the heat by electricity if nececcary, making it at worst as efficient as direct electric heating, which is what I’d use otherwise. Here like every other house has a heatpump like that and I don’t remember hearing anyone ever complaining that they’re not working.