I watch a streamer on YT who plays garbage games on steam and it's interesting wrt the game assets he's able to just call out what engine it was made with.
Once you've stared at them enough, the default PBR shaders in both Unity and Unreal combined with their environment/post-processing defaults make it very easy to spot.
Lighting and post-processing is a big tell too for those types of games. Unreal Engine has a default motion blur effect which is extremely obvious