Zu den schachen Schlüsseln haben sie auf Discoure Ubuntu bereits etwas geschrieben.
Das sind ab Noble Numbat die Anforderungen an die Algorithmen der Schlüssel:
rsa1024 für den Schlüssel gibt daher Mecker. Zitat aus den FAQ:
A PPA on Launchpad triggers a “weak algorithm” warning, what do I do?
PPAs are currently in the process of being upgraded to a 4096-bit RSA key and we expect that upgrade to be complete by release time. No action is needed (or possible) from PPA owners.
If you are currently using 24.04 before it is released, you will need to refresh the PPA signing keys when the warning becomes an error. We plan to provide easy functionality in add-apt-repository to do so, such that you do not need to remove and re-add the PPAs.
In the meantime, you may chose to ignore the warning or take it as a chance to reconsider which PPAs you have enabled.