Homebrew's default PostgreSQL uses your system user without a password.
On macOS, the default user setup for PostgreSQL varies based on the installation method, but the general best practices emphasize avoiding the default superuser for daily operations and using a dedicated, least-privilege user for your projects (source: google ai).
When managing PostgreSQL roles on macOS, the primary best practice is to implement the principle of least privilege by creating specific roles (users and groups) for different functions and granting them only the necessary permissions (source: google ai).
psql list databases\du\l