Yes, it should work (specs officially up to minus 20). Another alternative would be a socket switch that can measure consumption. And if it goes to 0 then you get a trigger

I also use the sensor in the freezer and it has worked without any problems so far.

I now have one in the freezer. Bosch, identical in construction to Siemens. The adjustable minimum temperature is -18, which results in a temperature of -20 (analogue thermometer). Unfortunately, the appliance does not allow warmer temperatures. Aqara knife hangs up at -18 and is then no longer active. No longer in the network. So I would say it goes up to max. -18, after that it's over.

Yes and no... :-) I have around 15 in use. 1-2 of them outside (protected) and one in the fridge and one in a freezer.
I have been using them for around 2-3 years now. On the ones that had to cope with lower temperatures or temperature fluctuations, I had to change the batteries much more frequently. You could literally see the battery charge level going down...
And I had to replace two of these sensors ("from the cold") after around 1 to 1.5 years.

Do you only get 1 for the price? You can get 4 on the net!