I think what makes something science fiction is whether enables you to understand a human problem by filtering through an alien lens.
Through our usual lenses, we can’t see the forest for the trees. It’s difficult to discuss issues or race, gender, colonialism, human identity, economics, politics and all the different ~isms because of our biases.
But put us in a different environment, invent technologies or other literary devices that enable us to push a situation to its extremes, then it clarifies our thinking. “What if we could…” or “What if we encountered…”
Science fiction has a couple of strategies. One is to use technology to push the limits. “What if we invent a machine where we could time travel?” “How much of a person can we replace before it stops being a person and stops being something else?” “What if your mind/psychological identity could be transplanted into a younger body regenerated from your own DNA?” “Who controls and receives the benefits of innovations and at what cost to others?”
The other strategy is about encountering “the other”. The alien. Maybe those of us who read sci-fi as kids and spent some time envisioning other cultures and what it means to see other worlds through other eyes, might embrace other cultures, races, and genders with curiosity rather than fear and oppression. Or maybe we’re content to fantasize about fucking sexy green female aliens with big boobs.
In SF the imagination is the limit; unfortunately, much of it is very limited. I don’t think it is technology or alien landscapes that define SF…those are just tools. I think rather it is a spirit of curiosity in a story where everything is just enough different that your initial biases are suspended and you, the reader, become alert to possibility.