My daughter is lactose intolerant, and drinks cow's milk just fine - the trick is that it's had lactase added, an enzyme that converts the lactose into, from memory, galactose and some other sugar.

Interestingly, lactase drops are also used when breastfeeding babies that have trouble with lactose (it can give them colic).

Nut-based milks are actually quite convincing, good even, but soy and oat milk... wow, don't know how anyone can drink those!