FTL aktualisieren und installer

[yubiuser]

Schau mal hier:

Can't update to FTL 5.9 Final: "Error: Unable to update package cache."

That's an issue with updating your OS rather than with Pi-hole: Your OS is informing you that the repository is now oldstable. Answering [y]es to that question or running sudo apt-get update --allow-releaseinfo-change should allow your OS to reflect that change and continue.