/etc/apparmor.d/usr.sbin.apt-cacher-ng is in apparmor-profiles-extra 1.19.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | # Author: Felix Geyer <debfx@ubuntu.com>
@{APT_CACHE_DIR}=/var/cache/apt-cacher-ng
#include <tunables/global>
/usr/sbin/apt-cacher-ng {
  #include <abstractions/base>
  #include <abstractions/nameservice>
  #include <abstractions/user-tmp>
  /etc/apt-cacher-ng/ r,
  /etc/apt-cacher-ng/** r,
  /etc/hosts.{deny,allow} r,
  /var/lib/apt-cacher-ng/** r,
  /{,var/}run/apt-cacher-ng/* rw,
  @{APT_CACHE_DIR}/ r,
  @{APT_CACHE_DIR}/** rw,
  /var/log/apt-cacher-ng/ r,
  /var/log/apt-cacher-ng/* rw,
  /{,var/}run/systemd/notify w,
  /{usr/,}bin/dash ixr,
  /{usr/,}bin/ed ixr,
  /{usr/,}bin/red ixr,
  /{usr/,}bin/sed ixr,
  /usr/lib/apt-cacher-ng/acngtool ixr,
  # Site-specific additions and overrides. See local/README for details.
  #include <local/usr.sbin.apt-cacher-ng>
}
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