The most plausible way to explode a planet is by a collision with another large astronomical object.
I don't know how large an impacting object would have to be to totally shatter an Earth-like planet.
The origin of the Moon is a scientific mystery since every theory of its origin has problems. the theory with the fewest problems which is most accpeted at the present is the giant impact theory.
The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planetesimal, approximately 4.5 billion years ago, in the Hadean eon (about 20 to 100 million years after the Solar System coalesced).1 The colliding body is sometimes called Theia, from the name of the mythical Greek Titan who was the mother of Selene, the goddess of the Moon.2 Analysis of lunar rocks, published in a 2016 report, suggests that the impact may have been a direct hit, causing a thorough mixing of both parent bodies.
So if the impact theory is correct an impact between an Earth sized world and a Mars sized world not always be enough to totally destroy the Earth sized world. Depending of variables such as the angle and the speed of the impact, the Earth sized would would sometimes or always survive more or less intact, though of course its surface would become an ocean of molten lava.
It is possible that a Mars size impactor would sometimes suffice to shatter an Earth size planet, depending on the angle or velocity of the impact. Or maybe an impactor would always have to be more massive than Mars to totally shatter an Earth sized planet.
Of course many present theories of solar system formation involve planets migrating inwards or aoutwards from the orbits where they formed. Thus it is possible for an Earth sized planet to collide with another Earth sized planet or with a super Earth, or a giant planet.
Thus it is possible to imagine as violent a collision as is necessary for an Earth sized planet to be completely shattered or to be swallowd up by a larger planet.
However, such collisions would have been far more likely to happen early in the history of the solar system, when gravitational interactions between forming planets caused some to be ejected from the solar system, others to fall into the Sun, and others to collide with other planets, until the only planets left were ones in orbits which would be stable for billions of years.
And of course a planet with human like inhabitants would have to be bilions of years old, since it should take bilions of years for intelligent life to evolve on a planet. And by then the probability of a collison between planets happening during the short period of maybe a few million years when there is intelligent life on one of those planets would be very small.
Of course there are countless billions and trillions of stars and planets in the universe, and in DC Comics like Superman a rather high percentage of them have planets with intelligent life, so statistically a planet with intelligent life would sometimes be destroyed by a planetary collision in the fictional universe of DC Comics. Whether such a collision would be likely to happen so close to Earth that people escaping from it would land on Earth is another question.
And there are rogue comets, asteroids, planets, and brown dwarfs which have been ejected from solar systems as mentioned above or which formed in interstellar space.
Just as it is possible, though statistically unlikely, for another star to collide with the Sun and destroy the solar system, it is possible for a rogue astronomical object large enough to destroy an Earth size planet if it hit it to pass thorugh the solar system and possibly collide with an object in the solar system.
In 2017 an interstellar rogue comet or asteroid called Oumuamua passed through the solar system, and in 2019 an interstellar comet called C/2019 Q4 (Borisov) was discovered passing thou rough the solar system.
In the novel Fifth Planet, 1963 by Fred and Geoffry Hoyle, a bright blue star is detected approaching the solar system. It passes so close to the Sun that several planets are switched between stars as they pass. I found it very hard to believe that any bright star which was going to come that close to the solar system within the next few millennia would not already be discovered and already be known to me.
But an interstellar comet or asteroid could enter the solar system and be detected only a short time before it makes its closest pass by the Earth - or collides with Earth. And since interstellar objejects would often have several times the relative speed of solar system objects a collision with an interstellar asteroid or comet, an impact from one of them might be several times as devastating as an impact with one that comes from our solar system.
And since rogue planets as large as Earth or bigger have been detected, it is certainly possible that one of them could enter the solar system unexpectedly and collide with Earth with comparatively little warning.
So it certainly would be theoretically possible for Kyrptonians to detect a rogue planet entering their solar system from interstellar space, and calculate that it would collide with Krypton, and perhaps some would try to escape from Krypton to other worlds in spaceships.
And as far as I can tell, that is just about the only scientifically possible method for a habitable palnet with an intelligent species to be shattered into pieces that would never rejoin.