I tried updating from ubuntu 18.04 to 20.04. It gave errors previously saying that third party applications were causing problems and then the it stopped midway. I turned off the repositories of third party apps in Software and updates. This time it just stated that 'Could not calculate the upgrade. An unresolvable problem occurred while calculating the upgrade.'
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38
ProcVersionSignature: Ubuntu 5.4.0-42.46~18.04.1-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.16
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Mon Aug 10 19:47:32 2020
InstallationDate: Installed on 2018-08-13 (727 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_IN
SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-08-10 (0 days ago)
VarLogDistupgradeTermlog:
mtime.conffile..etc.update-manager.release-upgrades: 2020-08-10T19:43:00.375714
It is not enough to just turn off sources for third party packages, you actually need to revert back to the official versions of the package from the Ubuntu archive. This can be done with the tool 'ppa-purge' and you'll need to at least do it for the kisak mesa packages you have installed.