permission denied to create and drop user

Hello all,

I have just installed postgresql on Debian stable (from debian apt
archives). It seems that the postgres user does not have permissions to
DROP/CREATE USER. I was expecting the postgres user to be a superuser but
something seems weird. my postgres user does not have the usual superuser
attributes.

Please see my results bellow:

root(at)deb10tp:/# id
uid=0(root) gid=0(root) groups=0(root)
root(at)deb10tp:/# pwd
/
root(at)deb10tp:/# su postgres
postgres(at)deb10tp:/$ psql
psql (11.9 (Debian 11.9-0+deb10u1))
Type "help" for help.

postgres=> DROP USER foo;
ERROR: permission denied to drop role
postgres=> DROP USER postgres;
ERROR: permission denied to drop role
postgres=> CREATE USER foo;
ERROR: permission denied to create role
postgres=> \du
List of roles
Role name | Attributes | Member of
-----------+------------+-----------
pgcon | | {}
postgres | | {}

How do I get a superuser/postgres that is capable to CREATE / DROP another
user? or a user that might allowed to do anything?

Thank you
Joao