Shortly after Star Wars came out back in the 1970s was the first time I heard the term science fantasy. With Star Wars fans, there are two groups – Group 1: Star Wars is science fiction; Group 2: it is science fantasy. I tend to avoid taking sides when the groups meet because no matter what side you take, the other side will take issue with your position. Personally, I think the first link below sums it best although Wikipedia makes the same point.
You can decide, but here are some links that address the differences between science fiction and science fantasy:
People love to debate what is “real” science fiction. Is hard SF the only real SF? Where is the line between soft science fiction and science fantasy, and should both simply be called fantasy?
According to the Henderson Institute of Knowing Knowledge, there are three general levels of science fiction. There used to be six, but one was erased in a time paradox, one was converted into pure energy, and one was confiscated by Area 51 and cannot be discussed. The three remaining levels are:
• Hard Science Fiction
• Soft Science Fiction
• Science Fantasy
The difference is that if the story includes a mix of possible science fiction (i.e. scientifically possible future or alternate events or technology) and something that is impossible (no matter how plausible the author makes it sound), then it is science fantasy.
This one is geared towards screenwriters and looks at Superman while briefly talking about Star Wars – https://www.writersdigest.com/writing-articles/by-writing-genre/science-fiction-fantasy/the-difference-between-science-fiction-and-fantasy-what-every-screenwriter-needs-to-know.
Then, there’s this one, https://www.goodreads.com/topic/show/797546-science-fantasy-vs-science-fiction which starts out with:
Can I just say that I hate the term “Science Fantasy”. I think it’s stupid and ignorant for anyone to say that grandiose science fiction is in some way not science fiction but instead is science fantasy.