Comment 2 for bug 1873423

It's not your .zshrc (which would be in your home directory) but the system's /etc/zsh/zshrc which has been deleted and tried to compare.

This issue seems though unrelated to the deletion of /etc/zsh/zshrc, with which at coped properly:

Configuration file '/etc/zsh/zshrc'
 ==> Deleted (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.

It seems not a zsh issue at all but a general release upgrade issue which just happened to happen while handling conffiles of the package zsh-common:

*** zshrc (Y/I/N/O/D/Z) [default=N] ? d
sh: 1: pager: not found
diff: standard output: Broken pipe

So for some reason, /usr/bin/pager (or /bin/pager or so) was not available during the release upgrade. /usr/bin/pager is usually /etc/alternatives/pager. Unfortunately, I have not really an idea against which package this could have caused. Reassigning to ubuntu-release-upgrader-core for now.