/etc/apt/apt.conf.d/20archive is in update-notifier-common 0.119ubuntu8.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | APT::Archives::MaxAge "30";
APT::Archives::MinAge "2";
APT::Archives::MaxSize "500";
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