Could not calculate the upgrade to 24.04

[Stéphane]

Following error message appears when I try to upgrade from 23.10 to 24.04:

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This was likely caused by:
 * Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If you want to investigate this yourself the log files in '/var/log/dist-upgrade' will contain details about the upgrade. Specifically, look at 'main.log' and 'apt.log'.

ProblemType: Bug
DistroRelease: Ubuntu 23.10
Package: ubuntu-release-upgrader-core 1:23.10.14
ProcVersionSignature: Ubuntu 6.5.0-35.35-generic 6.5.13
Uname: Linux 6.5.0-35-generic x86_64
ApportVersion: 2.27.0-0ubuntu5
Architecture: amd64
CasperMD5CheckResult: unknown
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Thu May 23 09:51:51 2024
InstallationDate: Installed on 2021-09-21 (975 days ago)
InstallationMedia: Ubuntu 20.04.3 LTS "Focal Fossa" - Release amd64 (20210819)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to mantic on 2024-05-23 (0 days ago)
VarLogDistupgradeTermlog:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.