cannot upgrade from 20.04 to 22.04

[Thomas Locher]

Error message:

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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'.
------------------------------------------------------------------------

I removed basically all PPAs but it still doesn't work.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.41
ProcVersionSignature: Ubuntu 5.15.0-94.104~20.04.1-generic 5.15.136
Uname: Linux 5.15.0-94-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.27
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Wed Feb 14 09:25:32 2024
InstallationDate: Installed on 2020-12-17 (1153 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to focal on 2024-02-14 (0 days ago)
VarLogDistupgradeTermlog: