Cannot update to 20.04LTS

[Thomas]

Following sudo do-release-upgrade

I get: An unresolvable problem occurred while calculating the upgrade.

Here are the details of the executions:

Checking for a new Ubuntu release
Get:1 Upgrade tool signature [1 554 B]
Get:2 Upgrade tool [1 342 kB]
Fetched 1 344 kB in 0s (0 B/s)
authenticate 'focal.tar.gz' against 'focal.tar.gz.gpg'
extracting 'focal.tar.gz'

Reading cache

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Hit http://fr.archive.ubuntu.com/ubuntu bionic InRelease
Hit http://fr.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit http://fr.archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit https://download.docker.com/linux/ubuntu bionic InRelease
Fetched 0 B in 0s (0 B/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done

Checking for installed snaps

Calculating snap size requirements

Updating repository information

Third party sources disabled

Some third party entries in your sources.list were disabled. You can
re-enable them after the upgrade with the 'software-properties' tool
or your package manager.

To continue please press [ENTER]

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Metadata [224 B]
Get:85 http://fr.archive.ubuntu.com/ubuntu focal-backports/multiverse amd64 c-n-f Metadata [116 B]
Fetched 42,4 MB in 6s (3 200 kB/s)

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating the changes

Calculating the changes

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'.

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 1:18.04.38
ProcVersionSignature: Ubuntu 4.15.0-118.119-generic 4.15.18
Uname: Linux 4.15.0-118-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.9-0ubuntu7.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Thu Oct 8 00:07:31 2020
InstallationDate: Installed on 2016-09-15 (1483 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-10-07 (0 days ago)