Is there any difference between the words magic and magick?
Fundamentally? No. Historically? Yes.
The "k" was added during the 19th-century occultist movement, a precursor to the 20th century witchcraft movement, as a means of differentiating magical (magickal?) rituals and spells from performative illusions aka stage magic. It was popularized by Aleister Crowley, among others, and the specialized spelling persisted into foundational texts for modern witchcraft. And these in turn influenced many other writers of modern witchcraft and pagan literature down through the decades, even to the present day.
Some people prefer to use the "k" spelling, others don't see a need. Personally, I don't like to use it because I don't think it's necessary and because it IS strongly associated with Crowley, who was a pretty notoriously racist asshat. This may or may not have anything to do with how the word "magic" is spelled, but I don't like to give him the time of day if I can help it.