I am unable to upgrade ubuntu 20.04, after sudo do-release-upgrade -d

[Peter Markos]

system reports

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

I have ubuntu 18.04 and did

sudo apt update
sudo apt upgrade
but nothing helped

Peter markos

lsb_release -rd
Description: Ubuntu 18.04.5 LTS
Release: 18.04

apt-cache policy pkgname
N: Unable to locate package pkgname

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38
ProcVersionSignature: Ubuntu 4.15.0-115.116-generic 4.15.18
Uname: Linux 4.15.0-115-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: XFCE
Date: Wed Sep 2 13:20:53 2020
InstallationDate: Installed on 2014-12-11 (2092 days ago)
InstallationMedia: Xubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140723)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-09-02 (0 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Klaus (kr11035)]

After first trying to upgrade with : do-release-upgrade -p
the result was :
An unresolvable problem occurred while calculating the upgrade.

This was likely caused by:
* Unofficial software packages not provided by Ubuntu
 I then unticked all " PPA 's "
the result was :
Could not determine the upgrade

An unresolvable problem occurred while calculating the upgrade.

Can't the upgrader indicate [ Which "Unofficial" software is a problem ? ]

My next option is to get a fourth hard drive installed on the PC and install 20.04.lts there.
[ I have drive 1 = Win XP , drive 2 = Win 7 , drive 3 = Ubuntu 18.04 LTS ]