I found the problem. Documenting here for posterity.
I had a file in /etc/apt/preferences.d/ containing this:
Package: *
Pin: Release v=18.04, -l=Ubuntu
Public bug reported:
Here's the error that I think describes the problem in /var/log/dist-
upgrade/main.log :
2021-04-02 21:21:20,082 DEBUG The package 'e2fsprogs' is marked for removal but
it's an ESSENTIAL package
2021-04-02 21:21:20,129 ERROR Dist-upgrade failed: 'The essential package
Public bug reported:
if you make a screen with screen -S foo you cannot then reattach it
via screen -R ftab with the current completion script. It only
completes if you start typing with the numeric ID from screen -ls, which
is not as easy to remember as the name you gave it (foo in this
** Patch added: patch to satisfy this feature request
https://bugs.launchpad.net/bugs/924676/+attachment/2704679/+files/screen.patch
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https://bugs.launchpad.net/bugs/924676
Title:
The code in the patch looks sane to me, and applied cleanly against my
installation of wordpress 2.9.2-1ubuntu1 (Lucid).
The patched WP's blog seems to work properly afterward; I restarted
Apache and logged in as admin, created a new post and 2 comments and
that worked fine.
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