I have not seen this warning before.

I am not terribly concerned about it, but I do not know about the
consequences of it in later distributions or going forward (because of
the usual systemd dependency issues).

A search for "postgresql unsupported distribution warning" didn't turn
up anything in the first couple pages.


...

Stopping PostgreSQL 13 database server: main.
Unpacking postgresql-13 (13.13-0+deb11u1) over (13.11-0+deb11u1) ...
Setting up libpq5:amd64 (13.13-0+deb11u1) ...
Setting up postgresql-client-13 (13.13-0+deb11u1) ...
Setting up postgresql-13 (13.13-0+deb11u1) ...
Starting PostgreSQL 13 database server: main.
Processing triggers for postgresql-common (225) ...
supported-versions: WARNING! Unknown distribution: devuan
debian found in ID_LIKE, treating as Debian
supported-versions: WARNING: Unknown Debian release: 4
...


From: https://www.postgresql.org/docs/current/supported-platforms.html

Documentation → PostgreSQL 16
Supported Versions: Current (16) / 15 / 14 / 13 / 12
PostgreSQL can be expected to work on current versions of these
operating systems: Linux.....

Regards,
Ken