I've read all the postings here including the one that said it was already answered and elsewhere for this apparently common problem but so far I have not been able to resolve it. The other answers did not help.
Typically I keep my systems up to date but this PC has been in storage for a year and a half during a remodel and now that it is back online, it needs to be updated/upgraded from the EOL 19.10 to 20.10 but it fails, then immediately wants to update again.
$ sudo apt update
Ign:1 http://us.archive.ubuntu.com/ubuntu eoan InRelease
Err:2 http://us.archive.ubuntu.com/ubuntu eoan Release
404 Not Found [IP: 91.189.91.38 80]
Hit:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:4 http://archive.canonical.com/ubuntu xenial InRelease
Hit:5 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Hit:6 http://archive.ubuntu.com/ubuntu xenial-security InRelease
Reading package lists... Done
E: The repository 'http://us.archive.ubuntu.com/ubuntu eoan Release' does not have 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.
