Kojima's bext game uses the same engine that Guerilla have used for Horizon.
Due to the connections there's 3 easter eggs connected to Death Stranding hidden in Horizon:
The Stranded Figure is found in the All Mother complex, and can be picked up anytime after the critical main path quest The Proving. Directions are in the video above.
The Stranded Necklace is found in The Grave-Hoard. This dungeon is in the north-east corner of the map, but you cannot enter until the critical path mission of the same name. It’s easily found by hugging the left wall from the entrance to the room where you fight your first set of enemies in this dungeon.
The Stranded Shackles are found in the Zero Dawn dungeon, which you can’t access till critical path mission Deep Secrets of the World. The shackles are found in the south-western part of the map after the second major holo-imager scene. See the video for more guidance.