The KTM Duke 250 is a compact motorcycle with a relatively low seat height. While it may not be specifically designed for taller riders, it can still accommodate riders of varying heights, including those who are 6.3 feet tall.
What might be comfortable for one rider may not be for another. It would be ideal for you to visit a KTM dealership or any location where you can sit on the bike and get a feel for its ergonomics and overall comfort.
During the test ride, pay attention to factors such as the legroom, knee bend, handlebar position, and overall riding position. Ensure that you have enough room to move around comfortably and that the bike doesn't feel too cramped. If possible, take the bike for a test ride to see how it performs and feels on the road.
Ultimately, it's recommended to assess your personal comfort on the Duke 250 by trying it out firsthand to ensure that it suits your specific height and preferences.