I don't think this is mandatory but government have been lobbying with supermarkets and they agreed to add doors about 8 years ago, probably to avoid being forced with a total ban.

You still see some small doorless fridges with high margin quick grab products but you no longer need to wear a coat when you go near the fresh or frozen department.

Part of this is not energy savings, but food safety - doorless fridges often have some products near the front that aren't kept to the required sub-5C. Meat products often require 0-3C nowadays too, which is an even narrower range and even harder to meet across all products in a doorless fridge.

Lower and more precise temperatures reduces food waste, which indirectly reduces both costs and energy use.

Over here in Germany I am seeing those fridges getting doors when supermarkets are being renovated as well. But still many open ones exist.

(While I assume that some of those are opened quite often, where shutting doors might push a lot of warm air back in, while keeping them open with less air movement might even be more efficient)

Where in France you buying refrigerated milk?

(Somewhat joking. I’m sure chilled milk is a thing, but I think shelf-stable UHT has like 95% of the market)

Almost any supermarket ;) You're right though, UHT is a big thing for some inexplicable reason.

UHT is a bit cheaper and of course, shelf stable. I understand the reason why it is so popular.

Personally, I use both. I usually buy a bottle or two of fresh milk when I go shopping, and I keep a pack of UHT in case I don't have enough fresh milk. This way, I will not run out of milk, and I will not let my fresh milk spoil because I bought too much.

And yes, fresh milk (whole and half-skimmed) can be found in almost any supermarket. AFAIK skimmed milk is almost exclusively UHT, and raw milk is very hard to find but not illegal.