>    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) ...