There are already a number of mods out there which alter the appearance of Fallout 4, but they don’t go quite as far as this tweak, which makes the game look like it came from Telltale (or Gearbox) instead of Bethesda.
It’s not a standalone mod; as Reddit_is_wrong (who made the screenshots) explains, they’re the result of some tweaks to the ENB injector SweetFX/Reshade, which as we’ve seen in other games (even older Fallout ones) can have a dramatic effect on a game’s visuals.
“I started off with a SweetFX preset for Fallout 4 and then tweaked the .ini file to turn on the “cartoon” cell shader”, they write. “You can customize the .ini file to your liking, how strong the border is...etc.”
If you want to try it yourself, here’s how to achieve the same effect, while this is a guide on how to do it in any game using ENB.