/etc/apt/apt.conf.d/20apt-show-versions is in apt-show-versions 0.22.7ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | // When Apt's cache is updated (i.e. apt-cache update)
APT::Update::Post-Invoke-Success {
"test -x /usr/bin/apt-show-versions || exit 0 ; apt-show-versions -i";
};
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