Can't upgrade to 20

[P Chen]

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 18.04
Package: ubuntu-release-upgrader-core 1:18.04.40
ProcVersionSignature: Ubuntu 5.4.0-54.60~18.04.1-generic 5.4.65
Uname: Linux 5.4.0-54-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.20
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Fri Nov 20 10:57:02 2020
InstallationDate: Installed on 2019-08-02 (475 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-11-20 (0 days ago)
VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

You don't seem to have the ubuntu-desktop package installed which then forced the release upgrader to consider your system a server. This may have resulted in the failure to calculate the upgrade. Please install ubuntu-desktop and try the upgrade again.

[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!