The Garou OPM manga is the original source, and the anime adaptation does a decent job of bringing it to life. It might compress or expand certain scenes, but the core elements remain intact. Fans of the manga usually appreciate the anime's efforts to recreate the world and characters.
Yes, the OPM manga has come to an end. The creators completed the narrative, providing closure to the fans. Although some might have hoped for more, what was presented was a comprehensive and conclusive tale.