Star Trek is true scifi? I always considered it to be soft scifi due to it being more about social issues in space rather than the more hard scifi about the fictional science. At least the book of Project Hail Mary is closer to hard scifi than Star Trek as they spend a lot of time describing the science. The movie rightfully skips most of this tedium in favor of a beautiful spectacle.
This is the first time I've heard of the idea of "true" scifi though.
Star Trek is largely fantasy.
IMO if "fantasy" tries to explain things as being technology, it's (soft) sci-fi. If it describes it as magic, then it's fantasy.
Technobabble is just tech-sounding magic.
They have different writing styles generally, but it is still pointless to call Star Trek a fantasy for the same reason why you wouldn't call Lord of the Rings a science fiction. If you have a spectrum from fantasy to science fiction with 5 being the middle then maybe Star Trek would be a 6 and Star Wars being more of a 5.
Personally I'd classify Dune to be more of a fantasy than Star Trek just because of the style it is written in being very mystical and prophetic.
For me it is a mix of things, i referenced Star Trek because author of the comment mentioned it in comparison. But for me fantasy is in the past in the "better times" and magic. SciFi for me looks into the future or alternative reality enhanced by technology.
Dune for me is SciFi, because space, spaceships, and very little magic. It is about comparison of societies rejecting and embracing technology, with little magic on top.