The game will be released in two separate versions for Sony's last and current-gen console, and only the more expensive special editions for the PlayStation 4 will receive a free upgrade to the PS5 version. For many fans of the game who are affected by the current shortage of PS5 consoles, this means that they would have to buy the game twice should they finally snatch a PlayStation 5.
https://www.notebookcheck.net/Horizon-Forbidden-West-No-free-PS5-upgrade-for-buyers-of-the-standard-PS4-version.558511.0.html