It is not unusual that a game is being developed for two generations of game computers. And games that make the transition to a new generation are also commonplace. However, games that don’t come to the older generation at release, but come later, are rare.
However, since the PlayStation 5 and Xbox Series X are still harder to find than a needle in a haystack, Observer: System Redux is now available on the PlayStation 4 and Xbox One. You can also upgrade this version for free if you still manage to get your hands on the new generation, so there is little reason not to.