The whole thread is a bit daft really.After all, EVs are not short of battery power to run them.
Heated mirrors just come with certain specs of car, EV or ICE. If you want them you buy one of the (usually higher) specs of the model you want that has them. Or in some cases buy the option pack that gets them.
And like ICE, some of the poverty spec models won't even have them as an option.
As with things like Android Auto or cruise control these extras gradually become mainstream or standard on more of the range as part of the 'war' between car makers to attract punters. So if you are looking at second hand then they will probably be harder to find as you are running a few years behind the 'norm'.