Not sure if that's a thing in France, but alternatively to plant milk for lactose intolerant

• Lactose-free milk (there are versions with lactose removed instead of broken down, that aren't sweet and taste basically the same as normal milk)
• Lactase enzyme taken together with the coffee, to break lactose down

I don't really see plant milk as the lactose-intolerant variant, but a vegan option, but that might just be due to the fact Finland has lactose-free milk available as an option basically everywhere as milk is such an important part of the coffee culture.