The only location Shield players can find a Sableye is in the Dusty Bowl in the Wild Area. However, the problem is a Sableye only shows up in this location when there's Heavy Fog. Making fog appear is extremely difficult, but you can reliably have it spawn after you've gone through and beaten the game.

Is Sableye in Pokemon sword?

Sableye is exclusive to Pokemon Shield. In Pokemon Sword, Sableye cannot be encountered in the wild, but can be obtained by trading.

Does Sableye evolve?

This Pokémon does not evolve.