There’s also different kinds of heat pumps. The most expensive version is vertical bore, but it also does better in colder climates. The term “heat pump” is kind of confusing to the average person, because it represents several different ways/layouts to accomplish the same goal.
Additionally, even if it can’t keep up in extreme cold weather (hypothetically), imagine if you have a system that can heat your home to 15C, and then you have supplemental heating on top of that. You’d still save money and energy over having traditional heating methods.
It’s all basically the same type of systems, it just varies as where they pull/send to. The vertical bore style is just straight down instead of loops in your backyard for the installations where there isn’t much yard to work with. It takes more specialized equipment because you’re drilling rather than just burying lines, hence most of the added costs.
Where I live it drops into the -30 to -40c degree temps and properly installed geothermal systems have no problems with it.