kittens start out lactose tolerant, just like humans, but then often develop lactose intolerance as they age and don't need to drink their mother's milk anymore. some cats are more tolerant than others, and for the intolerant ones you can give them lactose free milk (or "cat milk" which is lactose free cow milk with nutrients for cats)

if your cat likes regular cow milk but not lactose free milk though you should probably not give it regular milk anyway. lactose intolerance is a menace and even just the tiniest bit of unprocessed lactose can absolutely annihilate your gut, and cats don't often decide what's best for them in the long term.

All mammals lose the tolerance to lactose as they age. Except for a handful of mutants.

Maybe you're descended from one of them. Note that cheese was a way to store milk with very little lactose so it was edible by all.

Cat's milk doesn't have lactose.