unless I am very much mistaken this is only true for air source heat pumps. If you're in a cold environment I would expect you'd want a ground source heat pump instead, although the installation cost for that will be significantly higher than air source.

Mine works fine.

they still struggle under -20C. Which is not abnormal for many places in Canada

Yes, but that's why heat pumps in this country are typically paired with auxiliary electric heat. The heat pumps still contributes some amount, even at -30 or below, but the electric "tops up" the pre-warmed air that the heat pump makes.

And that is only really needed for a couple of months out of the year, even in places like Winnipeg or Edmonton.

20-30 years ago, the heat pump technology wasn't as capable, and couldn't do the job as well, but they have improves quite a lot since then.

I have a heat pump and furnace combo. The heat pump works extremely well down to around -10C. Below that it takes a very long time to move the needle by half a degree. The furnace doesn’t kick in until the thermostat sees the house temperature trending in the opposite direction it’s attempting to achieve.

Unfortunately, its method of determining the time gradient of temperature is rather moronic and doesn’t take the temperature schedule into account. This means every morning when the schedule calls for higher daytime temperatures (even by just half a degree) the thermostat freaks out thinking that the house is cooling rapidly and kicks on the furnace to bring up the temperature.

This causes the system to needlessly run the furnace every single morning. It annoys the hell out of me but I don’t know what to do about it. Aftermarket thermostats aren’t very common around here (Canada).

Central heat pumps have built in electric heat in cases the heat pump alone isnt sufficient.

Even if the heat pump isnt enough all the time, its still better than heating with oil, electricity, gas, etc. exclusively.

It isnt an all or nothing situation.

Last conversation I had on Reddit years ago a guy in Ottawa had data that showed that he was drawing heat during near -40C.

Some heat pump models can work at -30C

Many are designed for extreme temperatures now, but they are not efficient in such temperatures due to the properties of the refrigerants available. It will usually still run, but will run longer than usual and may not be able to keep up with heat demand. During a cold snap, might run continuously and may need frequent defrost cycles which further reduces efficiency and heating capacity. How cold they can/should go depends on things like sizing, refrigerant, building insulation, solar heat gain, and other factors. In a country like Canada, air source heat pumps will always be installed with a backup heat source. In Canada, that is most commonly the same natural gas furnace that the house was always originally equipped with, while the heat pump replaces the air conditioning unit, but backup heat can also be resistive electric, heating oil, wood, and more, and a decent thermostat will have an outdoor air sensor that can detect an appropriate outdoor conditions at which to switch from heat pump to backup/"emergency" heat when needed, and then back to heat pump when conditions permit.

In my experience, my heat pump provides about 90% of my heating from fall to spring. Only a few severe cold snaps put the heat pump on the bench for a few days switching over to emergency heat completely, and most of the winter it runs frequently to continuously to maintain consistent temperatures and only needs a short and occasional boost from the furnace. The gas backup is also nice peace of mind in case of a prolonged power outage due to a potential ice storm, as the furnace blower and electronic controls can easily be run off a small battery pack or generator for a very long time.

See here how Norway is doing it: https://www.theguardian.com/environment/2023/nov/23/norway-heat-pumps-cold-heating