Not upgraded from Ubuntu 16.04 to Ubuntu 18.04

[Ambikeya Pradhan]

(base) ambikeya@ambikeya-HP-ProBook-440-G2:~$ sudo do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]
Get:2 Upgrade tool [1,247 kB]
Fetched 1,247 kB in 0s (0 B/s)
authenticate 'bionic.tar.gz' against 'bionic.tar.gz.gpg'
extracting 'bionic.tar.gz'

Reading cache

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Hit http://archive.ubuntu.com/ubuntu xenial InRelease
Get:1 http://archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Get:2 http://archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]
Get:3 http://archive.ubuntu.com/ubuntu xenial-security InRelease [109 kB]
Fetched 325 kB in 0s (0 B/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done

The Robot Operating System (ROS) is installed

It appears that ROS is currently installed. Each ROS release is very
strict about the versions of Ubuntu it supports, and Ubuntu upgrades
can fail if that guidance isn't followed. Before continuing, please
either uninstall ROS, or ensure the ROS release you have installed
supports the version of Ubuntu to which you're upgrading.

For ROS 1 releases, refer to REP 3:
https://www.ros.org/reps/rep-0003.html

For ROS 2 releases, refer to REP 2000:
https://www.ros.org/reps/rep-2000.html

Are you sure you want to continue?

Continue [yN] y
No snaps are installed yet. Try 'snap install hello-world'.

Checking for installed snaps

Calculating snap size requirements

Updating repository information
Hit http://archive.ubuntu.com/ubuntu bionic InRelease
Hit http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit http://archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit http://archive.ubuntu.com/ubuntu bionic-security InRelease
Fetched 0 B in 0s (0 B/s)

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating the changes

Calculating the changes

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

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'.

Restoring original system state

Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.32
ProcVersionSignature: Ubuntu 4.15.0-142.146~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-142-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.30
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Wed Jun 16 14:46:52 2021
InstallationDate: Installed on 2019-01-12 (886 days ago)
InstallationMedia: Ubuntu 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2021-06-16 (0 days ago)