Darkness effect

I recetly played a game which has exactly the effect im looking for implemented. The games has all sorts of crazy visual tricks, but the one i'm interested in is the fade to suddden darkness in a kind of unrealistic way. The game is called Promesa and the theme is remembering/memories, so as the game progresses you can see more and more of the environments, and the blackness moves further away.

I'm just wondering how it could maybe be acheived in unity, cause i know it's not by placing lights carefully, and that it's not a static effect. I think it might be some kind of volume, but sometimes the fades are too gradual for that. So idk how it's acheived, but i'm sure some of you will know!

I've got some examples i recorded from the game, so you can see exactly how it works
1st is to show that it's not static
2nd is to show that the lighting acts as normal, when visible
3rd is to show how, again, the darknes doesnøt come from "natural" lighting within the game, and that the darknes isn't bleeding out of the barn.