I have tried several times to install the updtae evrsion from 18.04 to 20.04. Each time, I have the same answer : There was an unsolvable problem during the upgrade calculation. This was probably caused by: * unofficial software packages that are not from Ubuntu. Please use the "ppa-purge" command from the package "Ppa-purge" to remove packets from a PPA Launchpad repository, and then try to rerun the upgrade.

[Défarge]

There was an unsolvable problem during the upgrade calculation.

  This was probably caused by:
  * unofficial software packages that are not from Ubuntu.
Please use the "ppa-purge" command from the package
"Ppa-purge" to remove packets from a
PPA Launchpad repository, and then try to rerun the upgrade.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38
ProcVersionSignature: Ubuntu 5.4.0-52.57~18.04.1-generic 5.4.65
Uname: Linux 5.4.0-52-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: XFCE
Date: Mon Oct 26 15:18:28 2020
InstallationDate: Installed on 2019-12-23 (307 days ago)
InstallationMedia: Xubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-10-26 (0 days ago)
VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

Reviewing the files from your upgrade attempt you seem to have enabled a PPA that provides sane packages. This will prevent the upgrade as that PPA contains package version numbers greater than the release to which you are upgrading. You can revert the PPA by installing the ppa-purge package from the official Ubuntu archive and then running 'sudo ppa-purge ppa:sane-project/sane-git' or 'sudo ppa-purge ppa:sane-project/sane-release' . After that you can try upgrading again and if it still fails open a new bug report. Thanks and good luck!