PostgreSQL - How to login with my Linux user account

I'd like to log into my newly installed PostgreSQL [ PostgreSQL 12.15
(Debian 12.15-1.pgdg120+1) ] using my linux account.
In trying to do that this web page
<https://alvinalexander.com/blog/post/postgresql/log-in-postgresql-database/>suggest
that I enter :

psql -d mydb -U myuser -W

However, that command requires a database_name (mydb), and PosgreSQL 12.15 being so freshly installed does not yet
have any database created by me.

How would you suggest I circumvent this challenge?

Mind you that, using the postgres account I have created other accounts.

Role name | Attributes | Member of
-----------+------------------------------------------------------------+-----------
chispa | Superuser | {}
pedro | Superuser | {}
postgres | Superuser, Create role, Create DB, Replication, Bypass RLS | {}

Thanks in advance.