The Catfish Seamonster can be killed in Metro Exodus but it has to be done in a specific area of Volga.
Make your way to the east side of the map. This area is called the terminal and can be reached with boats nearby. Once you made your way through the maze-like hall inside, you come to a small room.
Inside is a bell, 3 wires to cut and a lever. Use them in the same order to kill the Catfish.
METRO EXODUS PLAYLISTS:
★ Guides – http://bit.ly/metro-exodus-guides