Hello there,
As we have had no reports of this issue with the installation error during “Seas of Fate” persisting for some time now, we will now be locking this thread.
If you have encountered this error in-game, can you first check that the installation of Assassin's Creed: Valhalla has been completed. You can check this by going to Notifications > Downloads on your console. If the game hasn't finished installing, please let the game fully install before playing any further. You should receive a notification when the game is fully installed.
If the game has been fully installed and you are still encountering this error, it could mean that the game files have been compromised due to the game being launched before installation completed. To troubleshoot this issue, please fully uninstall the game from your console. We then suggest that you try the troubleshooting steps provided on the support article for your console:
• PS4
• PS5
Please ensure that you restore the licenses and rebuild your console database. Then reinstall Assassin's Creed: Valhalla. If you own the physical version of the game, please first disconnect the console from the internet before installing the game. Once the game has been fully installed, reconnect to the internet, and allow the console to install any updates.
If the error continues to persist after trying those steps, the please feel welcome to create a new thread so we can take a closer look at this. Please confirm that you have been able to try these troubleshooting steps and provide an image/video of the error you’re receiving whilst progressing in “Seas of Fate.”
Thanks!