Ubuntu 20.04 to 22.04 upgrade fails

[Jean-Luc Aufranc]

The upgrade to Ubuntu 22.04 fails with the message:

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.

But I understand third-party ppa were disabled during the upgrade, so it's unclear where the issue is coming from. apt.log complains about gcc instead:

Investigating (0) libgcc1:amd64 < 1:10.3.0-1ubuntu1~20.04 @ii mK Ib >
Broken libgcc1:amd64 Depends on gcc-10-base:amd64 < 10.3.0-1ubuntu1~20.04 -> 10.4.0-4ubuntu1~22.04 @ii umU > (= 10.3.0-1ubuntu1~20.04)
  Considering gcc-10-base:amd64 5 as a solution to libgcc1:amd64 75
  Added gcc-10-base:amd64 to the remove list
  Fixing libgcc1:amd64 via keep of gcc-10-base:amd64
  MarkKeep gcc-10-base:amd64 < 10.3.0-1ubuntu1~20.04 -> 10.4.0-4ubuntu1~22.04 @ii umU > FU=0

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.40 [origin: unknown]
ProcVersionSignature: Ubuntu 5.15.0-60.66~20.04.1-generic 5.15.78
Uname: Linux 5.15.0-60-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.25
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Wed Mar 1 21:51:31 2023
InstallationDate: Installed on 2020-10-02 (880 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to focal on 2023-03-01 (0 days ago)
VarLogDistupgradeTermlog:

[Nick Rosbrook (enr0n)]

Reviewing the files from your upgrade attempt, you have installed nodejs from the nodesource PPA. This version of nodejs is greater than the one in the official archive and is keeping some packages installed which then prevents the upgrade from being calculated. Please remove nodejs along with any other packages from that archive and disable the archive. After that you can try upgrading again and if it still fails open a new bug report. Thanks and good luck!