sudo do-release-upgrade doesn't work

[ANTOR Md Ahsan Habib]

It says again & again """"Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

If none of this applies, then please report this bug using the
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.If
you want to investigate this yourself the log files in
'/var/log/dist-upgrade' will contain details about the upgrade.
Specifically, look at 'main.log' and 'apt.log'.
""""

Even though I removed all broken package. I don't know what to do now

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.30
ProcVersionSignature: Ubuntu 4.15.0-115.116~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-115-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.24
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Thu Sep 3 12:07:09 2020
InstallationDate: Installed on 2019-05-08 (483 days ago)
InstallationMedia: Ubuntu 16.04.6 LTS "Xenial Xerus" - Release amd64 (20190227)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2020-09-03 (0 days ago)