Fiction, without a doubt. Consider the sheer scale and the physical principles involved. The sun is an enormous fusion reactor. Its fate is dictated by factors like gravitational forces and the amount of fuel it has. Fiction allows us to explore the idea of stopping its explosion, but it remains in the realm of the imagination, far from scientific possibility.
These are definitely fiction. In reality, the sun's life cycle is a natural astrophysical process that we can't stop with stories. The sun is powered by nuclear fusion, and it will go through various stages like becoming a red giant in the future, which is a natural progression determined by its mass and the laws of physics.