Depends on what’s in it and what your goals are.
Obviously anything with like a bunch of calories is going to end your fast. As a general rule, if you’re fasting to achieve specific physiological states for health reasons, probably best to avoid. But if you’re fasting as a means to lose weight and control calories, you can probably get away with an unsweetened or artificially sweetened one. Though some folks still prefer to just do like a double shot of espresso instead.