Ubuntu 20.04.1 desktop upgrade crash from 18.04.4

[L. Csordas]

On a clean, up-to-date 18.04.4 machine I have been trying to install Focal 20.04.1 for 3 days with the update offered by the Update Manager

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.40
ProcVersionSignature: Ubuntu 4.15.0-121.123-generic 4.15.18
Uname: Linux 4.15.0-121-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Mon Oct 19 16:56:05 2020
InstallationDate: Installed on 2019-10-27 (358 days ago)
InstallationMedia: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=hu_HU.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-10-19 (0 days ago)
VarLogDistupgradeTermlog: