Alien/s invade/conquer/do bad things to Earth. They are so mysterious and unknowable that humans can barely guess at their motives. They do strange, magical-realist type things to Earth that makes human life much more difficult, or may kill many or all humans. In some examples, humans aren't able to resist effectively; in others, there's no way to even attempt it.
To be an example of this trope, the alien or alien's motives must never be revealed in the story.
Do We Have This One?
- Robert Silverberg's The Alien Years--invasion by beautiful aliens of unknown motives who defeat all attempts at resistance. Attempts to learn about them are even less successful.
- Brian Aldiss's "Heresies of the Huge God"--gigantic, non-sentient alien creature throws Earth off its orbit with its tail. (Humans react with medieval-type religious movements to try to propitiate this being.)
- At least two of Ian Watson's stories--"Slow Birds," in which objects float over Earth's atmosphere, glassing the surface, and "Cages," in which aliens (who don't come down to Earth) cause cages to appear over different parts of people's bodies. (Or they do other bizarre things to people that makes their lives hard--like the woman who can't see through one of her eyes, but her abusive boyfriend can see through that eye of hers.)
Not quite examples, but could be part of the same supertrope/s:
- Thomas M. Disch's The Genocides, in which aliens turn Earth into a monoculture agribusiness plantation (all growing the same crop). The humans are like insects to them, they are so powerful. However, their motive seems to be known.
- Solaris--not on Earth, and not an invasion. But the sentient alien planet is unknowable to humans, and remains so.