Thalos VI was the sixth planet in the Thalos system of the Alpha Quadrant.
The Ferengi Gaila was arrested there in 2374 for vagrancy. (DS9: "The Magnificent Ferengi")
This planet was only mentioned in dialogue.
This planet's quadrant of origin is inferred based on the position of its star system as seen in the star chart appearing in the Star Trek: Picard episode "Maps and Legends".
Gaila was subsequently detained on a Starfleet station, suggesting that the planet was under Federation jurisdiction.