Is it normal to not be able to whistle?
Yep.Totally normal
Yes—it’s normal not to be able to whistle. Some people never get the hang of it, and it usually doesn’t mean anything is wrong.
Whistling takes a particular shape and flow of air through your lips, and not everyone finds the knack. Plenty of people can’t whistle at all, or can only manage a breathy squeak no matter how many tutorials they try.
If you want to learn, experimenting with your lip shape and airflow may help—but there’s no special trick you’re failing to discover. If you used to whistle and suddenly can’t because of a new change in your mouth or face, that’s a different story; otherwise, it’s just one of those random human variations.