Ubuntu 20/10 updates stopped updating - where to dig?

Question

linux

All LXC containers running for me stopped receiving updates.
Where to dig?
Tips on the Internet are quite old and refer to other, earlier versions.
Thank you.

[email protected]:~# hostnamectl
   Static hostname: webpanel
         Icon name: computer-container
           Chassis: container
        Machine ID: c855a9be5702ba9392e5d44e5fb289f9
           Boot ID: f125e37ffd714214a38708687b94614b
    Virtualization: lxc
  Operating System: Ubuntu 20.10
            Kernel: Linux 5.4.157-1-pve
      Architecture: x86-64

apt update 
Ign:1 http://archive.ubuntu.com/ubuntu groovy InRelease
Ign:2 http://archive.ubuntu.com/ubuntu groovy-updates InRelease
Ign:3 http://archive.ubuntu.com/ubuntu groovy-security InRelease
Err:4 http://archive.ubuntu.com/ubuntu groovy Release
  404  Not Found [IP: 91.189.88.152 80]
Err:5 http://archive.ubuntu.com/ubuntu groovy-updates Release
  404  Not Found [IP: 91.189.88.152 80]
Err:6 http://archive.ubuntu.com/ubuntu groovy-security Release
  404  Not Found [IP: 91.189.88.152 80]
Reading package lists... Done
E: The repository 'http://archive.ubuntu.com/ubuntu groovy Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu groovy-updates Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://archive.ubuntu.com/ubuntu groovy-security Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Answer 1

Well, support for Ubuntu 20.10 ended in July 2021.
Update...