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?](https://askubuntu.com/q/1230856/1019605)

Therefore, I tried to reinstall the Ubuntu software by referring to the following [documents](https://askubuntu.com/questions/79987/how-to-re-install-software-center), 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

```