Science-Fantasy is a thing and Star Wars is a predominant example of it. Sci-Fi is a genre that deals centrally with the concept of technology and how that impacts society and the growth of humanity.

The main difference between Science Fiction and Fantasy are the questions "Could this happen? If so, is there an attempt to explain how?" Star Wars makes zero effort to explain itself and mostly handwaves away the idea of doing it. Lightsabers are just "elegant technology", starships exist and travel by "hyperdrive" with no pretense of the rules that govern them, and there's a mysterious "Force" that somehow binds living things together but is mostly used to make objects levitate somehow. Because nothing is really explained and it's just accepted, you can pretty easily change the setting to medieval times and not a whole lot changes - lightsabers become magic swords, starships become just ships, the Force is still perfectly workable. The stories don't change, only their clothes and architecture.

Contrast this with Star Trek, where the logistics of space travel are a huge plot point. Ships have realistic crews and command structures, politics and government make up the main drivers of plots, and there are adhered to rules about how the technology on the ship works. Later Trek started to get a bit more into the fantasy side of things, but Roddenbery's vision was always heavily sci-fi. Star Trek is built around the idea of how humanity functions in a future where we've figured out space travel - it really doesn't work if you take the technology out of it.