package otrs2 6.0.26-1 failed to install/upgrade: il sottoprocesso installato pacchetto otrs2 script post-installation ha restituito lo stato di errore 1

While advancing from 18.04 LTS to 20.04 LTS things got somewhat corrupted because of huge databases in mysql, myISAM tables.

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: otrs2 6.0.26-1
ProcVersionSignature: Ubuntu 4.15.0-163.171-generic 4.15.18
Uname: Linux 4.15.0-163-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.21
Architecture: amd64
CasperMD5CheckResult: skip
Date: Thu Dec 2 14:14:54 2021
ErrorMessage: il sottoprocesso installato pacchetto otrs2 script post-installation ha restituito lo stato di errore 1
InstallationDate: Installed on 2013-03-22 (3177 days ago)
InstallationMedia: Ubuntu-Server 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120817.3)
PackageArchitecture: all
Python3Details: /usr/bin/python3.8, Python 3.8.10, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: /usr/bin/python2.7, Python 2.7.18, python-is-python2, 2.7.17-4
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.6
SourcePackage: otrs2
Title: package otrs2 6.0.26-1 failed to install/upgrade: il sottoprocesso installato pacchetto otrs2 script post-installation ha restituito lo stato di errore 1
UpgradeStatus: Upgraded to focal on 2021-12-02 (0 days ago)