I saw a scene from a cartoon where a huge robot on four legs was walking through the wasteland and raking in the cities with its mouth. The robot also leaves traces turned backwards. Some man follows his tracks, gets inside and kills the pilot, and his girlfriend falls dead (from grief, I guess).
This is a bit of a long shot, but maybe Robot Carnival (1987)?
https://www.imdb.com/title/tt0093871/