These messages are defined in /usr/lib/update-notifier/apt_check.py with no flags to disable them.

Here's a sed command that will neuter the functions that generate the messages by inserting a return statement as the first line of the message function:

sudo sed -Ezi.orig 

  -e 's/(def _output_esm_service_status.outstream, have_esm_service, service_type.:

)/1    return

/' 

  -e 's/(def _output_esm_package_alert.*?

.*?

.:

)/1    return

/' 

  /usr/lib/update-notifier/apt_check.py

A diff of the old and new files looks like this:

$ diff -u /usr/lib/update-notifier/apt_check.py{.orig,}

--- /usr/lib/update-notifier/apt_check.py.orig  2023-02-22 11:33:39.476095290 -0500

+++ /usr/lib/update-notifier/apt_check.py   2023-02-22 11:59:41.396527682 -0500

@@ -160,6 +160,7 @@

 def _output_esm_package_alert(

     outstream, service_type, disabled_pkg_count, is_esm=False

 ):

+    return

     " output the number of upgradable packages if esm service was enabled "

     outstream.write("

")

     if disabled_pkg_count > 0:

@@ -206,6 +207,7 @@

 

 

 def _output_esm_service_status(outstream, have_esm_service, service_type):

+    return

     if have_esm_service:

         outstream.write(gettext.dgettext("update-notifier",

                                          "Expanded Security Maintenance for "

Test the fix with this command:

$ /usr/lib/update-notifier/apt_check.py --human-readable

1 update can be applied immediately.

To see these additional updates run: apt list --upgradable

Regenerate the cached message file

sudo /usr/lib/update-notifier/update-motd-updates-available --force