mysqld – Cannot init mysql server with config file

I tried to create MySQL database configuration file with the following content:

[mysqld]
port=3305
datadir=db/data
socket=db/mysql.socket
mysqlx=0
default_authentication_plugin=mysql_native_password

Next step i want to setup mysqld with this config:

mysqld --defaults-file=db.cnf --initialize-insecure

and i got the error:

mysqld: [ERROR] Failed to open required defaults file: /home/alexander/db.cnf
mysqld: [ERROR] Fatal error in defaults handling. Program aborted!

What am I doing wrong?