Comment 6 for bug 1741607

Please check your repositories.

I can't reproduce your issue on fresh Ubuntu MATE 20.04.3 LTS VM without any third-party repositories. I have successfully installed both PlayOnLinux and VirtualBox from Software Boutique.

```
$ cat /etc/os-release
NAME="Ubuntu"
VERSION="20.04.3 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.3 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

$ sudo snap refresh
All snaps up to date.
$ snap list
Name Version Rev Tracking Publisher Notes
core18 20210722 2128 latest/stable canonical✓ base
snapd 2.51.4 12883 latest/stable canonical✓ snapd
software-boutique 0+git.f633ffb 54 latest/stable/… flexiondotorg classic
ubuntu-mate-welcome 21.04.0-ef35c052 626 latest/stable/… flexiondotorg classic

$ grep -r ^deb /etc/apt/ --include=*.list
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal main restricted
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal-updates main restricted
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal universe
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal-updates universe
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal multiverse
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal-updates multiverse
/etc/apt/sources.list:deb http://archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu focal-security main restricted
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu focal-security universe
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu focal-security multiverse

$ sudo apt update -qq && apt list --upgradable
All packages are up to date.
Listing... Done

$ dpkg -l | grep -vE "^ii|\|^Desired|"
$
```

Please prepare full info about your system and post topic about your problem on http://ubuntu-mate.community/ to get help.
Current bug is fixed. Your last comment is not about a bug, so LP is a wrong place for rants like "Who is responsible...".
Testers are always welcome, you can play your role nicely anytime.