Internet-Security.com UDP port 27019 details

Valve Steam uses UDP 27019 as part of its documented Steam/Steamworks networking ranges (UDP 27000–27031 and 27014–27050) for gameplay traffic, matchmaking, server queries, and peer connectivity.
Real-world software that can use this port via Steamworks includes CS:GO, Dota 2, and Team Fortress 2 (among many other Steam-based titles).
In practice, you’ll see UDP 27019 in use on Steam clients and Steam-hosted game servers as part of their normal network operations.

UDP 27019