Recently, I completely erased the old disk data and installed the 20.04 LTS version of Ubuntu. However, Ubuntu software is not working properly. Also I can't even install the software. Please refer to the following: Why don't appear categories items in Ubuntu Software?

Therefore, I tried to reinstall the Ubuntu software by referring to the following documents, but the following error occurred:

Hit:1 http://security.ubuntu.com/ubuntu focal-security InRelease              

Hit:2 http://kr.archive.ubuntu.com/ubuntu focal InRelease                     

Get:3 http://kr.archive.ubuntu.com/ubuntu focal-updates InRelease [89.1 kB]

Hit:4 http://kr.archive.ubuntu.com/ubuntu focal-backports InRelease

Get:5 http://kr.archive.ubuntu.com/ubuntu focal-updates/main i386 Packages [648 B]

Get:6 http://kr.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages [2,000 B]

Fetched 91.8 kB in 2s (44.6 kB/s)

Reading package lists... Done

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Package software-center is not available, but is referred to by another package.

This may mean that the package is missing, has been obsoleted, or

is only available from another source



E: Package 'software-center' has no installation candidate

+ Update-1

The installed pkgs:

ii  appstream                                  0.12.10-2                             amd64        Software component metadata management

ii  brltty                                     6.0+dfsg-4ubuntu6                     amd64        Access software for a blind person using a braille display

ii  docbook-xml                                4.5-9                                 all          standard XML documentation system for software and systems

ii  espeak-ng-data:amd64                       1.50+dfsg-6                           amd64        Multi-lingual software speech synthesizer: speech data files

ii  gnome-software                             3.36.0-0ubuntu3                       amd64        Software Center for GNOME

ii  gnome-software-common                      3.36.0-0ubuntu3                       all          Software Center for GNOME (common files)

ii  gnome-software-plugin-snap                 3.36.0-0ubuntu3                       amd64        Snap support for GNOME Software

ii  libdv4:amd64                               1.0.0-12                              amd64        software library for DV format digital video (runtime lib)

ii  libespeak-ng1:amd64                        1.50+dfsg-6                           amd64        Multi-lingual software speech synthesizer: shared library

ii  libqpdf26:amd64                            9.1.1-1build1                         amd64        runtime library for PDF transformation/inspection software

ii  libtss2-esys0                              2.3.2-1                               amd64        TPM2 Software stack library - TSS and TCTI libraries

ii  python3-software-properties                0.98.9                                all          manage the repositories that you install software from

ii  software-properties-common                 0.98.9                                all          manage the repositories that you install software from (common)

ii  software-properties-gtk                    0.98.9                                all          manage the repositories that you install software from (gtk)

ii  xbrlapi                                    6.0+dfsg-4ubuntu6                     amd64        Access software for a blind person using a braille display - xbrlapi

+Update-2

Snap-list:

Name               Version                     Rev   Tracking         Publisher     Notes

chromium           81.0.4044.122               1123  latest/stable    canonical✓    -

core18             20200311                    1705  latest/stable    canonical✓    base

gimp               2.10.18                     252   latest/stable    snapcrafters  -

gnome-3-28-1804    3.28.0-16-g27c9498.27c9498  116   latest/stable    canonical✓    -

gnome-3-34-1804    0+git.2c86692               27    latest/stable/…  canonical✓    -

gtk-common-themes  0.1-36-gc75f853             1506  latest/stable/…  canonical✓    -

libreoffice        6.4.3.2                     177   latest/stable    canonical✓    -

snap-store         3.36.0-74-ga164ec9          433   latest/stable/…  canonical✓    -

snapd              2.44.3                      7264  latest/stable    canonical✓    snapd