We're used to the classic depiction of a humanoid, maybe with a different color or height or a different number of fingers (ET), with higher-than-average intelligence.

What if they're just skilled at driving their "vehicles" and can't really reason or think or talk?

What if they're more like rabbits or sharks or pigeons or mushrooms or rocks?

What if they're invisible to the human eye? Maybe they are mostly transparent like jellyfish, who knows.

For all we know, maybe UFOs are the alien equivalent of drones. Unmanned (should I say unaliened?).

Maybe government(s) just know aliens are real, but they are fundamentally different from us and cannot be seen at all without some specialized equipment, or maybe they can be seen but they look like average living beings on Earth. Or maybe they just know someone is remotely driving those UFOs but we've never actually come close to seeing them.