ERROR: must be owner of table, but I am superuser

I have an postgres 16 DB in Docker container with volume. I wanted to hide standard postgres user and changed it's name to super (as example). Now I try to make something with any tables (DDL operations like ALTER TABLE) but it throws:

must be owner of table ...

I tried to give some privileges to my user but it throws for all commands:

permission denied

I have tries:

ALTER USER super WITH SUPERUSER;

But got:

Only roles with the SUPERUSER attribute may alter roles with the SUPERUSER attribute.

Then I run query:

SELECT rolname, rolsuper FROM pg_roles WHERE rolname = 'super';

It shows me:

rolename | rolesuper
--------------------
super    | true

Well. My role is superuser. I've even tried:

ALTER ROLE super SET ROLE super;

But it still shows:

Only roles with the SUPERUSER attribute may alter roles with the SUPERUSER attribute.

I cannot understand what can I do to fix that and have DDL or SUPERUSER role.

Solution

Well, one sleepless night and I found the answer. Let's inspect my docker compose file I use to deploy my app with db:

networks:
  app-network:
    driver: bridge

services:
  app-db:
    container_name: 'app-db'
    image: postgres:16
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_DB: postgres
      POSTGRES_HOST_AUTH_METHOD: md5
    ports:
      - "5432:5432"
    networks:
      - app-network
    volumes:
      - postgres-data:/var/lib/postgresql/data

  app:
    ...

I've renamed postgres user in db to super but I did not renamed it in docker compose file. I thought if I have a db container volume, all data will be stored in it, including users and roles. And it was but... It seems that superuser has its own rules. So now my postgres db knows about super user. It knows that it is SUPERUSER, but it is not, because on fresh deploy with docker-compose up DB was created not by super, but by postgres user (from docker compose file). When I changed pg user credentials to super in docker compose file, it works fine. Also, I don't want to store my credentials in docker compose file, because I want to store this file in git repository. So I change db credentials in this file before any deploy from now on. Thanks everyone and good luck!