Release upgrade to 20.04 LTS fails

[Javier]

I get the following message:

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'.

Restoring original system state

Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.37
ProcVersionSignature: Ubuntu 4.15.0-99.100-generic 4.15.18
Uname: Linux 4.15.0-99-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.14
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Mon May 4 20:02:08 2020
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-05-04 (0 days ago)

[Brian Murray (brian-murray)]

Reviewing the files from your upgrade attempt you seem to have enabled a PPA that provides Xorg and python packages. This will prevent the upgrade as that PPA contains packages which generate failures when trying to calculate the upgrade. You can revert the PPA by installing the ppa-purge package from the official Ubuntu archive and then running 'sudo ppa-purge ppa:oibaf/graphics-drivers'. After that you can try upgrading again and if it still fails open a new bug report. Thanks and good luck!