Yes, upgrading with the new version works!
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https://bugs.launchpad.net/bugs/1877761
Title:
Upgrading to new LTS 20 from LTS 18 via command update-manager -d
To manage notifications
Public bug reported:
Description:Ubuntu 18.04.4 LTS
Release:18.04
Error message says
This was probably caused by:
* Unofficial software packages not published by Ubuntu
Use the "ppa-purge" tool from the ppa-purge package
to remove software from a Launchpad PPA and
try to upgrade