:ppa keep coming back / unable to upgrade 18.04 > 20.04

[neo]

Hello ,

i have tried to upgrade my Ubuntu System from 18.04 to 20.04.

having problems deactivating the PPA that i have installed manually as requested by the upgrade process manager > however i try to do it, after a reboot, they are back.

ppa: skype and ppa:deadsnakes

tried deleting the manually (in "Software & Updates" >> "Other Software")
and via "ppa-purge" .

everytime it seems clean, i reboot, restart the upgrade the process (via "Software Updater")

then after some short time update fails with

error : could not calculate the upgrade.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.41
ProcVersionSignature: Ubuntu 5.4.0-56.62~18.04.1-generic 5.4.73
Uname: Linux 5.4.0-56-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.20
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Thu Dec 10 22:19:24 2020
InstallationDate: Installed on 2020-11-28 (12 days ago)
InstallationMedia: Ubuntu 18.04.5 LTS "Bionic Beaver" - Release amd64 (20200806.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-12-10 (0 days ago)
VarLogDistupgradeTermlog:

[Chris Guiver (guiverc)]

Thank you for taking the time to report this bug and helping to make Ubuntu better.

You may find help with your problem in the support forum of your local Ubuntu community http://loco.ubuntu.com/ or asking at https://askubuntu.com or https://ubuntuforums.org, or for more support options please look at https://discourse.ubuntu.com/t/community-support/709