Invalid Package Information during upgrade to 21.04

[Puneet Khurana]

After updating your package information, the essential package
'ubuntu-minimal' could not be located. This may be because you have
no official mirrors listed in your software sources, or because of
excessive load on the mirror you are using. See /etc/apt/sources.list
for the current list of configured software sources.
In the case of an overloaded mirror, you may want to try the upgrade
again later.

Then, when I tried to install ubuntu-minimal in another terminal window, it says that ubuntu minimal is already the newest version

Reading package lists... Done
Building dependency tree
Reading state information... Done
ubuntu-minimal is already the newest version (1.459).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubuntu-release-upgrader-core 1:20.10.15
ProcVersionSignature: Ubuntu 5.8.0-51.57-generic 5.8.18
Uname: Linux 5.8.0-51-generic x86_64
ApportVersion: 2.20.11-0ubuntu50.6
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
Date: Sun May 2 14:30:38 2021
InstallationDate: Installed on 2020-08-14 (260 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_IN:en
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_IN
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to groovy on 2021-05-02 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2021-05-02 14:30:02.877291
 Log time: 2021-05-02 14:30:12.758567
 Log time: 2021-05-02 14:30:35.442442
 Log time: 2021-05-02 14:30:38.049853