It's pretty rare for it to get above 25C where we live in Scotland - pretty sure it didn't get that warm at all this year.

If we relax "never" to "not more than 60 days a year", that would be most of Canada, northern US, most of Europe and Russia. No idea what's going on in southern hemisphere, but I guess Argentina/Chile and southern Australia are the same.

This obsession with mold looks to me as an exclusively US thing. I have no first-hand data but I guess it's due to insufficient air flow combined with air conditioners pushing humidity all the way up.

I was talking about internal temperature.

Cold climate results in low humidity. If you're mostly heating your home (as opposed to running aircon 24/7), air inside tends to be of lower humidity than outside. So low that it becomes uncomfortable and one has to use humidifiers.

The only place mold has any chance in those conditions are the leak spots on the fridge door seal.